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ELECTRICITY I 



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HENRY AND HORA'S 

MODERN 
ELECTRICITY 



A PRACTICAL WORKING ENCYCLOPEDIA 

A MANUAL OF 

THEORIES, PRINCIPLES AND APPLICATIONS 

BY 
JAMES HENRY, M. E. 

PROFESSOR OF ELECTRICAL ENGINEERING 

KAREL J. HORA, M. Sc. 

EXPERT ELECTRICAL ENGINEER 



A Text-book for Students, Apprentices, Artisians, Engineers 

Static and Current Electricity — Batteries — Measuring Instruments — Direct 
and Alternate Current Machinery — Transformers— Converters — Power 
Stations — Electric Railways — Telegraph— Electric Light — Tele- 
phone — "Wireless Telegraphy — Electroplating — X-Rays 
— Radium— Practical Estimates and Calculations 
EXHAUSTIVE CROSS-INDEX 



150 ILLUSTRATIONS 
TWO SPECIAL WIRING DIAGRAMS 




1915 

Chicago, U. S. A. : Laird & Lee, Inc. 



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Copyright 1904, by William H. Lee, 
Copyright 1915, by Laird & Lee, Inc. 



[ ALL RIGHTS RESERVED ] 



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MAR -8 1915 

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INTRODUCTION 



r^\ ROB ABLY no one branch of modern science has accomplished so 

much for the development of a higher civilization as electricity. 

Less than a century ago, this mysterious force was practically 

> unknown. At present there is scarcely a country or a town of any 

% size where it is not utilized in some form, and yet its possibilities are 

N still but dreams. The next quarter-century no doubt will revolutionize 

the present method of generating and transforming electricity into 

motive force. 

No field of industry offers the young man as many or as great oppor- 
tunities as that of electrical engineering. Men of technical education, 
men of practical experience in the various branches of electrical engineer- 
ing are in constant demand. 

Many of the works relating to the subject, seem to lack the practical 
knowledge necessary for everyday use. Theoretically correct, they lack 
the practical instruction essential to a thorough knowledge of electrical 
science. 

Henry and Hora's Modern Electricity has been prepared 
with a view of meeting every emergency that might confront the electri- 
cal engineer and inventor. In this volume every effort has been made to 
simplify the information, without sacrificing its clearness or accuracy, so 
that every apprentice and artisan will be able to gain a complete 
knowledge of the fundamental principles and applications of electricity. 

Each formula is explained in the clearest manner possible, and the 
processes of arriving at results have been mathematically demonstrated. 

The work will be found eminently practical, scientific and accurate. 

The illustrations have been prepared especially for this work, and 
represent the most modern forms of electrical devices and appliances. 

That Modern Electricity will answer the requirements of those for 
whom it is intended, and that it will meet the unqualified approval of 
every student, apprentice and artisan is the earnest desire of 

THE AUTHORS. 



INDEX 



Accumulator, 39. 

Alternate currents — cfiemical effect, 159. 

measurement, 160. 

pressure of, 150. 

Alternating currents, 103, 162. 

machines, 149. 

Alternators, 169. 

— armature of, 174. 

— coupling, of, 175. 

— field excitation, 172. 
magnets, 172. 

— types, 170. 

Aluminum, reduction of, 296. 
Ampere turns, 142. 
Angle of lag, 154. 
Appendix. 347. 
Arc— Voltaic, 228. 
Armature, 128. 

— winding, 140. 
Arrester — lightning, 195. 
Automatic self-regulation, 166. 

Batteries, 32. 

— cell arrangement, 45. 

— Edison, 43= 

— secondary, 39, 44. 

— storage, 42. 
Bells— electric, 220. 

— magneto, 225. 
Booster, The, 169. 
Box— starting, 195. 
Brilliancy of arc, 229. 
Brushes, 139. 
Buildings, wiring of, 219. 

Cables — submarine, 257. 
Calculation— ampere turns, 142. 
Calcium carbide, 298. 
Candle-foot, 246. 



Candle power, 231. 
Carbon, 231. 
Carborundum, 298. 
Cells — arrangement of, 45. 

— constants, 38. 

— dry, 37. 

— gravity, 37. 

— storage, 40. 
Central exchange, 266. 

Chemical effect— alternate current, 150. 

— equivalents, 51, 52, 53. 

— symbols, 354. 
Choking coils, 159. 
Circuits, 62, 237. 

— breaker, 192. 

— magnetic, 130. 

— opened and closed, 253. 

— polyphase, 177. 
Cleaning solutions, 293. 
Coefficient —of self-induction, 156. 
Coherer, 280. 

Coil — choking, 159. 

— induction, 104. 
Compound wound dynamo, 138. 
Condenser— arrangement of, 122. 

— electrical capacity, 28, 120. 

— testing, 123. 
Conductance, 59. 

Conductors and non-conductors, 19. 

— table of, 19. 
Connections for lamps. 243. 
Controller, 199. 

Copper equivalents of steel rails, 352. 

— plating, 291. 

— refining, 294. 
Corrosion of pipes, 347. 
Crookes tubes, 302. 
Current— alternating, 103, 162. 



Vll 



Vlll 



INDEX 



Current and pressure, 295. 

— effective, 159. 

— polyphase, 176. 

— pressure curve, 150. 

— thermo-electric, 75. 

— for plating, 292. 
Cut-outs, 194. 

Depolarization— chemical, 35. 

— electro-chemical, 36. 

— mechanical, 34. 
Detector— ground, 226. 

— lineman's, 225. 
Diplex telegraphy, 256. 
Distribution, 203. 
Drop in mains, 243. 
Duplex telegraphy, 254. 
Dynamo, 100, 126, 133, 135. 

— series, shunt, compound wound, 137. 

— Siemen's, 173. 

Efficiency of a motor, 144, 351. 

— of dynamos, 351. 
Electric arc, 234. 

— bells, 220. 

— heating, 300. 

— light and power transmission, 330. 

— meters, 108. 

— railway, 185, 196, 200, 315. 

— smelting, 297. 

— welding, 298. 
Electrical energy, 23. 

— discharges, 301. 

— engineering, 314. 

— lighting, 228. 

— machines, 23. 
Electricity, 15. 

— Production of, 16; static and cur 
rent, 17; positive and negative, 18; 
conductors and non-conductors, 19; 
induction, 20; energy, 23, 70. 

Electrodynamometer, 113. 
Electrolysis, 50, 289, 347. 
Electromagnet, 89. 
Electromagnetic inertia, 152. 

— disturbance, 277. 



Electromagnetic induction, 100. 
Electromagnetism, 85. 
Electrometer, 112. 
Electro-metallurgy, 289. 
Electroplating, 289, 293. 
Electrotyping, 294. 
Electrolytic refining, 294. 
Electroscope, 21. 
Equivalents, 51, 52, 53. 
Estimates on electric railways, 324, 346. 
Ether, 274, 277. 

Fall of potential, 67. 
Faraday's laws, 53. 
Faults— in lines, 253. 

machines, 185. 

wires, 221. 

Field magnets of alternators, 172. 
Filaments, 238. 
Friction machine, 24. 

Galvanometer, 110. 
Gold plating, 292. 
Ground detector, 226. 

Hot-wire instruments, 117. 
Hydraulic analogy, 26, 149. 

Induced pressure, 101. 
Induction, 20. 

— coil, 10L, 264. 

— electro: uagnetic, 100. 

— magnetic, SI. 

— motor. 17£>. 

— self, 1C5, 152. 

coefficient of, 156. 

Inductive capacity, 124. 
Impedance, 156. 
Instruments— hot-wire, 117. 

— Morse, 249. 
Insulation, 211. 

— resistance, 116. 

Joule's law, 72. 
Jack, The, 267. 

Key— telegraph, 250. 

Lag— angle of, 154. 



INDEX 



IX 



Lamps, 232. 

— incandescent, 237. 

base and socket, 240. 

connections, 243. 

fiiament, 238. 

principle, 238. 

rating of, 243. 

life of, 241. 

— mercury vapor. 244. 
Lenz's law, 105. 
Lighting, electric, 228. 
Lightning, arrester, 195. 
Line faults in, 253. 

— telegraph, 252. 

— testing, 222. 
Lineman's detector, 225. 
Locating a ground, 224. 
Location of transformers, 167. 

Machines— alternating current, 149. 

— classification, 133. 

— faults in, 185. 

— friction, 24. 
Magnetic circuit, 130. 

— induction, 81. 

— field, 83. 

— substance, 82. 
Magnetism, 80. 

— measure of, 84. 
Magneto-bells, 225, 264. 

— generator, 264. 
Magnetomotive force, 93. 
Marconi's telegraph, 284. 
Material for electric railway, 322. 
Measuring alternate current, 160. 
Measurements, 107, 245. 
Mercury vapor lamps, 244. 

Meters, 107; voltameter, 54, 109: volt- 
meter. 118; galvanometer, 110; watt- 
meter, 118; electrometer, 112; elec- 
trodynamometer, 113. 

Metric system, 352. 

— equivalents, 353. 
Microphones, 263. 
Morse alphabet, 249. 

— instrument, 249. 



Motor, 100, 133. 

— efficiency. 144. 

— induction, 178. 
Multiplex telegraphy, 254. 

Nickel plating, 291. 

Ohm's law, 58. 
Overhead wires, 213. 

Permeability, 90. 
Plating, 292. 
Plug, The, 267. 
Polarization, 34. 
Polarized relay, 255. 
Polyphase circuits 177. 

— currents, 176. 
Potential, 23, 67. 
Power stations, 185, 327 . 
Practical points, 186. 
Pressure, 101, 159, 230, 295. 

— for plating, 292. 

Questions and answers, 22, 30, 55, 76, 
97, 106, 124, 146, 184, 227, 247, 273, 288, 

Radium, 301, 311, 313. 
Radiographs, 308. 
Rail welding, 299. 
Railway curves, 326-7. 
Rating of lamps, 242. 
Receiver, 261. 
Refining copper, 294. 

— silver, 296. 

Reduction of aluminum, 296. 
Recording register, 251. 
Regulating mechanism, 233. 
Relay, The, 252. 

— Polarized, 255. 
Resistance, 60, 62. 

— insulation, 116. 

— of wire, 61. 
Rheostat, 113. 
Roentgen's rays, 302. 

Saturation curve, 91. 
Secondary battery, 39. 
Self-induction, 105, 152. 



INDEX 



Series wound dynamo, 137. 

Shunt wound dynamo, 138. 

Silver plating, 289. 

— refining, 296. 

Siemens' dynamo, 173. 

Sine curve, 150. 

Solenoid, 87. 

Specific inductive capacity, 124. 

Standard of resistance, 60. 

Starting box, 195. 

Storage battery, 42. 

Submarine cables, 257. 

Subscriber's sets, 265. 

Switchboard, 189, 266, 269. 

Switches, 193. 

Telegraph, The, 248. 
Telegraphy— automatic and autograph- 
ic, 256. 

— wireless, 281, 284, 285. 

— diplex, 256. 

— duplex, 254. 

— multiplex, 254. 
Telephone, The, 258. 

— common battery system, 271. 

— automatic system, 272. 

— induction coil, 264. 

— switchboard, 266, 269. 
Temperature and brilliancy of arc, 229. 
• — co-efficient, 60. 

Terrestrial magnetism, 81. 

Testing condenser, 123. 

Thermo-electric current, 75. 

Three-wire system, 204, 355. 

Torque, 144. 

Transformers, 164. 

Transmission and distribution, 203, 330. 

Transmitter, 261. 

Trolley, 198. 



Tubes, constancy of, 310. 

— life of, 309. 
Two-wire system, 203. 

Undergiound wires, 214. 
Units of work and power, 68. 

— table of electrical. 107. 

Vacuum, 240,301. 
Vat, 290. 
Vibrations, 275. 
Voltaic arc, 228. 

— cell, 32. 

— pile, 32. 
Voltameter, 109. 

— water, 54. 

Water voltameter, 54. 

Wattmeter. 118. 

Waves, 274, 277. 

Weight and capacity of cars, 326 

Welding electric, 298. 

— rail, 299. 

Wheatstone's bridge, 114. 
Wire, the, 206. 

— carrying capacity, 209. 

— faults in, 221. 

— overhead, 213, 

— properties of, 208. 

— resistance. 61. 

— size, 207. 

— tests, 210. 

— underground, 214. 
Wiring buildings, 219. 
Wireless telegraphy, 281, 284, 28& 

X-rays, 301, 303, 309, 311. 

Zinc, 38. 




THOMAS A. EDISON 

THE WORLD'S GREATEST ELECTRICIAN 



MODERN ELECTRICITY 



CHAPTER I. — Introduction 

Electricity 

i. The true nature of electricity has not yet been dis- 
covered. Many think it a quality, inherent in nearly all the 
substances, and accompanied by a peculiar movement or 
arrangement of the molecules. Some assume that the phe- 
nomena of electricity are due to a peculiar state of strain 
or tension in the ether which is present everywhere, even in 
and between the atoms of the most solid bodies. If the latter 
theory should be the true one, and if the atmosphere of the 
earth is surrounded by the same ether, it may be possible to 
establish these assumptions as facts. The most modern sup- 
position regarding this matter, by Maxwell*, is that light itself 
is founded on electricity, and that light waves are merely 
electro-magnetic waves. The theory " that electricity is 
related to, or identical with, the luminiferous ether," has 
been accepted by the most prominent scientists. 

But while electricity is still a mystery, much is known about 
the laws governing its phenomena. Man has mastered this 
mighty force and made it his powerful servant ; he can 
produce it and use it. 

*James Clerk-Maxwell, a celebrated Scotch physicist (I831-1879), first called 
attention to the fact, that the velocity of light waves (185.000 miles per second) 
and of electricity seem identical. Experiments made since, chiefly by Hertz, 
have demonstrated that electric waves have all the properties of light waves. 
They can be reflected, refracted, polarized, brought to a focus, etc. 

15 



16 MODERN ELECTRICITY 

2. Its simplest effects were observed by the ancient 
Greeks. Thales of Miletus, who flourished about 600 B. C, 
noticed that amber, when rubbed with silk, attracted light 
bodies, as bits of bran or cork. The name "electricity" is 
derived from elektron, the Greek for amber. The word was 
first used in 1600, by Dr. Gilbert, a famous English scientist, 
who proved before a large assembly in Colchester, that 
diamonds, crystals of minerals, glass, and sealing wax, had 
the same peculiarity as amber. He also mentioned the fact 
that moist air prevented good results in his experiments. 
The phenomena of electricity are attraction and repulsion, 
heat, light, mechanical destruction, and chemical decomposition. 
They have been known In part for considerable periods, but 
all their practical applications are of recent origin. 

Production of electricity 

3. Electricity is generated by mechanical or chemical action 

(a) Friction. (See § 5.) 

(b) Percussion. A blow by one substance on another pro- 
duces opposite electrification on the two surfaces that come 
in contact. 

(c) Vibration. Vibration produced in a rod of iron coated 
with an insulating substance produces opposite electricities (in 
the rod and the coating). Experiments made by Volpicelli. 

(d) Disruption. If a playing card is torn in two pieces, 
both pieces prove to be electrical. 

(e) Cleavage. Quick cleavage of mica produces sparks 
in a dark room. 

(f) Crystallization. Sulphur melted by heat and then left 
to cool and crystallize, becomes electrified when in process 
of crystallization. 



ELECTRICAL ENGINEERING \*J 

(g) Evaporation. When water evaporates, the liquid pos- 
sesses the opposite electrification of the vapor. 

(h) Combustion. Burning charcoal proves to be electrified. 

(I) Pressure. Cork when pressed with guttapercha or 
metals proves to be + (plus) electrified, while the gutta- 
percha or metals are — (minus) electrified. 

(j) Heating of crystals. Tourmaline and other crystals, 
when heated or cooled, become electrified. (Such crystals 
are called pyro-electric.) 

(k) Atmosphere. The atmosphere is always charged with 
more or less electricity. 

(1) Some animals are provided with an electric organ 
which they bring into action when touched by an enemy. 
Torpedo, gymnotus, and malapterurus are fish possesing 
powerful electric organs. 

(m) The roots and juice of plants are — , the leaves +• 

(n) Dissimilar metals when brought into contact produce 
opposite electrification. 

(o) Heating the junctions of two dissimilar metal rods 
produces opposite electrification in them, and electricity 
flows from one metal rod across the junction to the other. 

(p) Contact of two dissimilar liquids. 

(q) Contact of a liquid and a metal. 

(r) Chemical action of a liquid on two dissimilar metals, 

(s) Movement of a conductor in a magnetic field {magneto- 
electricity.} 

Static and current electricity 

4. There are two states of electricity, static and current. 
The first is electricity at rest, the second is electricity in 
motion. The difference between them is not well defined, 



18 MODERN ELECTRICITY 

and the laws governing the two kinds are about the same. 
Static electricity includes the facts known to the ancients. 
There is, however, one important difference : Current electri- 
city seems to flow through the substance of the conductor; 
Static electricity remains always on the surface of the charged 
body, as, for instance, in a hollow cylinder it is found on the 
outside or convex surface. The reason for this difference is 
unknown, but it is probably closely connected with the nature 
of the two kinds of electricity. 

Positive and negative electricity 

5. A glass rod rubbed with silk in dry air, becomes charged 
with an electricity called positive, while a rod of sealing-wax 
or other resinous substance, rubbed with wool or fur produces 
an electricity called negative. These terms were first em- 
ployed by Benj. Franklin, instead of the old names vitreous 
and resinous electricity. That this distinction is not made 
without a difference, can be proved in the following manner: 

Two balls of light material, as pith, are attracted to a 
charged glass rod, adhere to it, become charged themselves 
and then are repelled and fly off. They also repel each 
other, when charged and suspended in close proximity, but 
are attracted by a charged rod of sealing-wax. 

From these facts the following general law is deduced : 

RULE 1 . — A body charged with one kind of electricity repels 
one charged with the same kind, and attracts one charged with 
the opposite kind. 

6. The silk and wool, with which the rods were rubbed are 
affected in the reversed sense ; the silk used to rub the 
glass is found to be negatively electrified, and the wool with 



ELECTRICAL ENGINEERING 



19 



which the sealing-wax was rubbed is found to be positively 
excited. From this fact we deduce another general rule : 

- RULE 2. — Whenever a positive charge is developed, an 
equal negative charge is also developed and vice versa. 

7. But silk does not produce positive electricity in all other 
substances; sulphur, for instance, becomes negatively charged 
if rubbed with silk. In the following series, materials are 
enumerated in such an order that by rubbing together any two 
materials named, the one mentioned first will generally become 
positively charged : fur, wool, certain resinous substances, 
glass, cotton, silk, wood, metals, sulphur, certain other resin- 
ous substances, India-rubber, hard rubber. 

Conductors and non=conductors 

8. Metals become electrified by mere rubbing, but if the 
piece of metal is held in the hand while rubbing it, the elec- 
tricity flows into the human body as fast as it is produced. 
This can be avoided by fastening the metal in a frame or 
handle of dry wood or hard rubber. Materials which allow 
electricity to flow through them, or in other words, which 
conduct electricity, are called conductors ; materials that 
conduct electricity only slightly or not at all, are termed non- 
conductors Or INSULATORS. 

TABLE OF CONDUCTORS. 



GOOD. 


PARTIAL. 


NON-CONDUCTORS. 


I. 

2. 

3- 
4- 

5- 

6. 

7- 


silver (best) 

metals 

charcoal 

graphite 

acids 

salty solutions 

water 


8. animal bodies 

9. plants 

10. cotton 

1 1 . dry wood 

12. marble 

13. paper 


14. oil 

15. porcelain 

16. silk 

17. wool 

18. resin 

19. shellac 


20. sulphur 

21. ebonite 

22. paraffine 

23. glass 

24. dry gases 

25. air 


Dry air is a perfect 


or absolute insulator or isolator. 



20 MODERN ELECTRICITY 

9. A conductor is said to be insulated, when it is supported 
on insulators in such a way that electricity cannot flow or 
escape from it, — as by placing it on a plate of glass, or on 
feet of glass or other insulating material, 

Induction 

10. If two bodies, as brass balls, both insulated, and one 
electrified, the ether not, are placed near together, the other 
will also be found to become electrically charged, by induc- 
tion. The side near the first ball will hold the opposite kind, 
and the other side will show the same kind of electricity as 
the first ball holds. If a finger is held close to the further 
side of the second ball, the electricity on that side passes into 
the body of the person, leaving the ball charged with the 
opposite kind of electricity. This charge will spread over the 
whole ball, if it is removed from the neighborhood of the first 
ball. If, however, the two balls are brought into contact, the 
two charges will join, balancing, and thereby destroying, each 
other. This proves that the two charges, the inducing one 
and the induced one, are equal to each other. 

ii. It can be proved, furthermore, that the attraction of 
light bodies, as pith balls, by charged bodies, is caused by 
induction. The glass rod or sealing-wax first charges the pith 
ball by induction, half positively, half negatively. One half is 
attracted, the other half is repelled. The attracted half is 
nearer the inducing body than the repelled half, and, there- 
fore, the force of attraction is greater than that of repulsion. 

12. The unit of quantity of electricity is the coulomb, 
named after a French physicist who lived 1736-1806. Each 
coulomb in one charged body attracts or repels each coulomb 
in the other. Therefore: 



ELECTRICAL ENGINEERING 21 

RULE 3. — The total attraction or repulsion is equal to 
the number of coulombs in one multiplied by the number in 
the other, 

The intensity of attraction or repulsion between two 
charged bodies, then, is determined, first, by the product 
of the quantities of electricity in the two bodies ; second, 
by the material between them ; and third, by the distance 
between them. 

The electrostatic unit of quantity is the quantity which, when 
placed at a distance of one centimeter in air from an equal 
quantity, repels it with a force of one dyne. 

EXAMPLE 1. 

Two spheres charged with 4 and 6 units respectively are 
placed 2 centimeters apart. What force will they exert on 
each other? 

Solution : 

Any result equals the force divided by the resistance. 
The force is 4 multiplied by 6 ; therefore the resistance must 
be 2 multiplied by itself. 

4X6 

2^2 = 6 dynes. Ans 

Electroscope 

13. An electroscope is used to discover the 
presence of a charge ; an electrometer meas- 
ures the quantity of electricity in a charge. 
An electroscope is necessarily a very sensitive 
instrument. The one shown in fig. 1 consists 
of a glass jar, through the stopper of which a FlG> L 

brass rod extends into the interior of the jar. At the lower end 
of the brass rod two narrow strips of gold leaf are attached. 




22 MODERN ELECTRICITY 

m 

hanging straight down. As soon as any body, as a stick of 
sealing-wax, charged in the slightest way, is brought near 
the upper end of the brass rod, the two strips of gold leaf 
will fly apart, and if the charge is strong they will tear. 
This is caused by induction: the upper end of the brass 
rod becomes charged positively at the approach of the 
negatively charged sealing-wax, and consequently the two 
pieces of gold leaf are charged negatively and repel each 
other. 

Questions and Answers 

Q. Name a few common manifestations of electricity? 

A. When the air is dry and hair is combed with a rubber 
or metal comb, the hairs rise toward the comb and are repelled 
by each other. A faint crackling noise is heard, and If it 
is dark, minute sparks may be seen. Dragging the feet quickly 
over a woolen carpet and then approaching a conducting body 
with a finger, a spark will show, which in some instances has 
been utilized to light the gas. The lightning in the clouds is 
such a spark of enormous size and length. 

Q. How do like charges of electricity affect each other? 

A. They repel each other. 

Q. What efect have unlike charges of electricity upon each 
other ? 

A. They attract each other. 

Q. If metal is rubbed with silk, with what kind of electricity 
will it be charged? 

A. The metal negative, and the silk positive. 

Q. If metal is rubbed with India-rubber, with what kind of 
electricity will it be charged ? 

A. The metal positive, and the India-rubber negative. 



CHAPTER II. — Electrical Machines 

Potential 

14. When two electrically charged bodies are connected by 
a wire, electricity will flow from one to the other, until they 
are charged alike. The body from which the electricity flows 
is said to have a higher electrical potential. This fact may 
be illustrated by a comparison. If we connect two vessels of 
water with different levels by a pipe, water will flow into the 
vessel with the lower level, until the two levels are the same. 

The body from which the electricity flows is said to be 
positively charged, the other negatively. "Positive" means 
here: above the common level or average, and "negative" 
means below ; just as + and — mean above zero and below 
zero on a thermometer scale. Of course, the two charges are 
positive and negative, of higher and lower pressure, only in 
relation to -each other (relative potential). They may both be 
higher or lower than a charge in some other body, just as two 
bodies of water of different level may both be higher or lower 
than the sea level. The electrical level (zero) corresponding 
to the sea level in physics, is assumed to be the average elec- 
trical pressure of the earth's surface, and the electrical press- 
ure of a conductor is reckoned to be the difference between 
its potential and zero. 

Electrical energy 

15. in general, the amount of electricity actually utilized in 
the form of mechanical power or work done, is small as com- 
pared with the energy spent, but it is economical nevertheless, 
because it allows mechanical power to be transmitted over 

23 



24 



MODERN ELECTRICITY 



long distances, and through its several effects accomplishes 
results not to be achieved in any other way, except at a much 
greater expense of labor. 

Electrical energy is not used in the same quantity for all 
purposes. For some purposes it is used in the form of a small 
quantity falling through a great difference of potential while for 
other purposes we must have a large quantity of electrical 
energy falling through a small difference of potenial. Lightning 
consists in the passage through the air of a current of electri- 
city under enormous pressure. Thunder is the noise made by 
the electric spark called lightning which heats the air in its 
path, causing sudden expansion and compression followed by as 
sudden a rush of air into the partial vacuum thus produced. 

16. Kinetic energy does not enter into the question of 
electricity, because kinetic energy is the result of a substance 
in motion. Potential energy is stored up and ready to be 
brought into play, as the elasticity in a bent bow, or the 
weight of a pendulum at the turning-points at the extremi- 
ties of the oscillation. It is tendency to motion, Kinetic energy 
is the result of actual motion. 



SILK 



OJSHfON 



COMB 

BRASS CYLINDER 



)=0 



Friction machine 

17. The oldest 
type of these ma- 
chines is the cylinder 
electric machine. 
A glass cylinder re- 
volves around its 
axis which is turned 
FlG# 2< by means of one or 

two wooden handles. On one side there is a leather cushion 
covered with amalgam of zinc or tin pressing against it. and a 
piece of silk extending from this cushion covers the upper 




ELECTRICAL ENGINEERING 



25 



part of the cylinder. On the other side there stands a brass 
cylinder, with a rod extending toward the glass cylinder and 
provided with sharp points (like a comb), See fig. 2. 

Turning the handle we produce friction between the glass 
and the cushion, and thus a + charge on the glass cylinder 
and a — charge on the cushion. The + electricity is collected 
by means of the comb as follows : 

The + (plus, positive) charge of the upper surface of the 
glass cylinder, revolving toward the comb repels the + charge 
of the comb, which keeps passing into the brass cylinder, 
leaving the comb — (minus, negative) charged. The + elec- 
tricity of the glass cylinder is thus neutralized by the -elec- 
tricity of the comb, and the lower half of the cylinder remains 
uncharged, until it returns to the cushion, by the friction of 
which it is charged again with + electricity. The cushion is 
usually connected with the "earth" by means of a chain. 

The earliest form of this machine was designed by Otto von 
Guericke of Magdeburg, who used a sulphur ball instead of the 
glass cylinder, and his own 
hand instead of the cush- 
ion. Sir Isaac Newton, 
Von Bose, Winkler of Leip- 
zig, Gordon of Erfurt, De 
la Fond, Planta, Ramsden, 
Cuthbertson, Toepler and 
Holtz aided in the develop- 
ment of this machine. 

A combination of two 
disks, one stationary and 
one revolving, and two conductors, connected by a wire, (a 



ftfc/OUUNG PLACE 




.SECTOR 



-COMB 



Fig. 3. 



26 MODERN ELECTRICITY 

so-called Holtz Machine, see fig. 3), will produce a steady flow 
of electricity. Such a machine generates a small quantity 
of electricity, but the pressure is very great. 

Hydraulic analogy 

18. The flow of electricity may be explained by comparing 
the electric machine to a pump for circulating water through 
a system of two tanks with two connecting pipes. Electricity 
is not a fluid, of course, and the comparison is only made for 
the purpose of illustrating the manner of working, not to explain 
the nature of electricity. We can substitute the pipe for the 
wire, flow of water for current, pressure or head for voltage, 
friction for resistance, gallons delivered for amperes, valves for 
switches, safety valve for fuse, pipe fittings for contacts 
(joints), pressure gauge for volt meter and the water meter for 
watt meter. In velocity electricity can be compared only to 
that of sunlight, traveling 186,000 miles per second, and being 
nearly instantaneous. 

It will be helpful to the student to familarize himself with 
the following parallel : 

Water Electricity 

Pressure 

If the water in two tanks If any two conductors, elec- 

of any diameters stands at tricaily connected, hold elec- 

the same level, there will be tricity at the same potential, 

no flow through a connecting there will be no current. But 

pipe. But if the level in one if the potential is higher in 

tank is higher, water will flow one conductor, an electric 

to the other until the two current will flow toward the 

levels are at the same height, other, until the two potentials 

The flow is caused by press- are equal. The flow is caused 



ELECTRICAL ENGINEERING 



27 



ure due to difference of level by pressure due to differ- 

The quantity of water in each ence of potential. The quan- 

tank is immaterial. tity of electricity in each con- 

The pressure of one pound ductor is immaterial. 
per sq. inch is taken as the One volt is used as the unit 

unit of pressure. of difference of potential. 

Resistance 
The current of water in the The electric current in a 

pipe is resisted by friction circuit has to overcome the 



against the interior surfaces 
of the pipe, couplings, valves, 
etc. This resistance is the 
higher, the longer the pipe 
and the smaller its cross-sec- 
tion. 



resistance of the material 
( low conductance meaning 
high resistance). The longer 
the wire and the smaller its 
cross-section, the higher the 
resistance. One ohm is the 
unit of electric resistance. 
Intensity 



The strength of the current 
is equal to the pressure di- 
vided by the resistance. The 
unit of flow of water is either 
one cubic foot or one gallon 
of water per second. 

If the two tanks are con- 



The intensity of the current 
is equal to the difference of 
potential, divided by the re- 
sistance. The unit of intens- 
ity is one ampere, produced 
by the pressure of one volt 
against one ohm. 

If two similar electric cells 
nected by two pipes of equal are connected in parallel (see 
dimensions, the pressure and §47), the pressure and resist- 
resistance will be divided be- ance will be divided between 
tween them, that is, the totals them, and will, therefore, re- 
will remain the same. The main the same. The intens- 



28 MODERN ELECTRICITY 

flow of water will be doubled, ity will De the sum of the 

two intensities. 

If several tanks are con- If several electric cells are 

nected in a line, so that their connected in series (see § 47), 

water levels descend in steps, the pressure of the battery 

the pressure equals the sum equals the sum of the press- 

of all the pressures, and the ures of all the cells, and the 

resistance will equal the sum total resistance equals the 

of all the resistances. The sum of all the resistances, 

flow per second wili remain The current equals that of 

the same. one cell, 



Condenser. Electrical capacity 

19- A condenser is a device, consisting of two conductors 
with large surfaces separated by an insulator. The conductors 
are called the plates or coatings, and the insulating material 
is called the dielectric. A simple condenser consists of two 
sheets of tinfoil pasted upon the two surfaces of a piece of 
mica. The mica insulates the two sheets of tinfoil from 
each other. If the two plates are given opposite charges, one 
positive and the other negative, each of the charges, by induc- 
tion, increases the capacity of the other plate, by raising their 
relative potentials, that is their difference in electrical pressure, 
as to each other, as explained in § 14. (This may be com- 
pared to increasing the capacity of a water tank by adding to 
its height.) A condenser is charged by charging one plate 
positively, and by putting the same quantity of negative on 
the other plate. This is done very simply by 'connecting each 
plate with one pole of an electric machine, or by connecting 
one plate with the "earth" (ground), and charging the other. 



ELECTRICAL ENGINEERING 



29 



This subject of condensers is highly important, because 
every insulated wire may be considered to be one plate and 
the earth the other, while the rubber covering of the wire, or 
the surrounding dry air, is the dielectric. 

20. RULE 4. — The capacity of a condenser equals the 
combined capacity of the two plates. 

The capacity of condensers is the greater, 

(a) the larger the metal plates or coatings, 

(b) the thinner the dielectric between them, 

(c) the higher the dielectric capacity of the dielectric. 

The unit of electrical capacity is the farad. A conductor 
is said to have a capacity of one farad, if the pressure in it 
is raised to a potential of one volt by one coulomb, that is, 
if the transfer of one coulomb from one plate to the other, 
changes the difference of relative potential by one volt. 
But such a capacity (of one farad) is enormous. It never 
really occurs in the electrical industries. As the practical unit 
of capacity, therefore, the micro-farad (from the Greek 
mikros,sma\\) is used, being the one millionth part of a farad. 
The farad was named after Michael Faraday, the eminent 
English scientist (1791-1867), who discovered the fact that 
pressure is induced by moving a conductor across a magnetic 
field, and who may, therefore, be considered the primary 
inventor of the dynamo. 

The quantity of electricity in a charged condenser equals 
the capacity of the condenser (in farads), multiplied by the 
difference of potential between the plates (in volts). 

21. A Leyden jar is a condenser, the glass jar forming the 
dielectric, and the inside and outside tinfoil coatings, on about 



30 



MODERN ELECTRICITY 




Fig. 4. 



two thirds of its height, forming the plates. A brass rod 
terminating in a knob connects below with the inner coating, 
usually by means of a loose chain. The glass sur- 
face above the coatings is usually varnished, for 
better insulation. See fig. 4. A number of such 
jars having all the inner coatings connected, and 
also all the outer coatings, so that they may be 
charged and discharged together, is called a battery. 
See fig. 5. 

Questions and Answers 

Q. Does 'positive' and 'negative' mean the same 
in this chapter as in Chapter I ? 

A. It does not. In the first chapter the terms 
are used to distinguish between vitreous (positive) and resinous 
(negative) electricity. In this chapter, and in general, 
"positive" means "of the higher potential" and "negative" 
signifies "of the lower potential." expressing merely a differ- 
ence in electrical pressure. 

Q. Which is the positive pole of a cell? 

A. That from which the current flows 
through the connecting wire to the other pole. 

Q. Does the current in the cell flow from 
the negative plate to the positive ? 

A. It does, to complete the circuit. In a 
zinc-copper cell the copper plate is always 
called the positive plate, as it would be only confusing to call 
it positive above the liquid, and negative in the liquid. 

Q. Describe a Holtz machine ? See fig. 3. 

A. The Holtz induction machine has two disks of glass 
mounted close together, one of which rotates. The stationary 




Fig. 5, 



ELECTRICAL ENGINEERING 21 

disk has two openings pasted over with paper. These papers, 
or sectors, are charged, one positive, the other negative, with 
the aid of rods of glass and sealing-wax, or in some other way. 
In front of the revolving plate, opposite each sector there is a 
row of points (comb), each comb being connected with a con- 
ductor provided with an adjustable knob. The electricity in 
the sectors excites the combs and -conductors; from the combs 
the electricity flows into the revolving disk, which carries the 
charges from one comb to the other, acting inductively on the 
combs, and the charges are in turn neutralized by them. If 
the knobs of the conductors touch, a flow of electricity con- 
tinues, as long as the disk revolves. If they are separated, 
a spark will fly from knob to knob, completing the circuit. 

Q. How long does a lightning stroke last ? 

A. An infinitely short time. The impression it makes on 
the eyes lasts very much longer, and is, therefore, deceiving. 

Q. Can you give an instance which proves this ? 

A. The spokes in a wheel revolving so fast, that the human 
eye cannot recognize the spokes in ordinary light, are plainly 
seen in a dark night by the flash of lightning. 

Q, What is the principle of a condenser? 

A. It seems that the close proximity of the plates enables 
them to hold a larger quantity of electricity. 

Q. Does this mean an increase in the voltage ? 

A. No. A water tank of a larger diameter will hold a larger 
quantity of water than another, other things being equal, but 
if the bottoms and water surfaces in the two tanks are at the 
same level, they will have exactly the same pressure. 

Q. After whom was the ampere named ? 

A. After Ampere, a French scientist, who lived 1775-1836. 



CHAPTER III.— Batteries. 

Voltaic cell and Voltaic pile. 

22. An electric cell is an apparatus by means of which 
heat generated by chemical action is converted into an elec- 
tric current. This heat is generated in a way similar to the 
heat of burning wood. The carbon in burning combines with 
oxygen from the air and this chemical combination is accom- 
pained with the generation of heat. In a cell a metal combines 
with an acid, also giving off heat. 

A simple cell is constructed in this way : A glass vessel 
containing an acid or a salt solution, and two plates, one of 
zinc, one of copper are placed in the liquid at a distance from 
each other and connected outside the vessel by a wire. This 
is called a voltaic cell, in honor of its inventor, 
Volta, an Italian scientist, 1745 1827. Several such cells, 
connected in series, (the zinc of one cell connected with the 
copper of the next, and the zinc of the last 
connected with the copper of the first.) constitute a 
battery. See fig. 7. 

23. A voltaic pile is a battery consisting of a 
pile of disks of zinc, disks of cloth moistened with 
acid, and disks of copper, stacked up alternately in 
the order named. Each set of 3 disks constitutes 
a battery cell, and when the top copper disk is 
connected by a wire with the bottom zinc disk, a 
current flows through the wire. The pressure 
equals the sum of all the differences of potential in the 
several cells ; the more cells, the more pressure. See fig. 6. 

32 





ELECTRICAL ENGINEERING 



33 




Fig. 7. 



The uppermost copper piate is called the positive pole, 
because the current flows from it through the connecting 
wire to the lowest zinc plate. 

The electrical pressure, or electro- 
motive force (E. M. F.), developed by one 
Voltaic cell has been chosen for the unit 
of measure of electrical pressure, and is 
called a volt. Strictly speaking, the volt 
is about one ninth less than the pressure 
in a Voltaic cell with zinc and copper 
plates in diluted sulphuric acid. 

24. The acid attacks and eats into the 

zinc, undergoing a chemical combination with it. This chem- 
cal process goes on with a giving off of heat, the heat is con- 
verted into another kind of energy, an electric current, and the 
electricity then flows as long as the chemical action continues. 
— The zinc plate is called the negative plate, and the copper 
plate the positive. Similarly, in cells having plates of other 
metals, the plate most readily attacked by the acid is always 
termed negative, Usually the negative plate is of zinc, while 
the positive plate is of copper, carbon or platinum. The 
liquids commonly used are various acids, solutions of sal- 
ammonia, caustic potash cr other compounds in water. 

Another name for the poles is electrodes; the liquid is cal- 
led electrolyte (lytos, from the Greek, meaning ''dissolving.") 

25. A pump lifts water against a difference of pressure ; in 
the same way, the chemical action in the cell drives the cur- 
rent from the negative zinc plate through the liquids to the 
positive copper plate, against the difference of potential. 

A large cell does not give a higher pressure than a small 



34 MODERN ELECTRICITY 

one, the pressure depending exclusively on the nature of the 
liquid and the plates. This can easily be proved : If two cells 
of unequal size are made up from the same materials, and the 
copper plates connected, and also the zinc plates, — there will 
be no current, a proof that the two electrical pressures in the 
two cells, working in opposite directions, neutralize each other, 
that is, are equal. 
Polarization 

26. The hydrogen gas contained in the sulphuric acid is lib- 
erated by the chemical action (see § 48) and settles on the 
copper plate in bubbles. These bubbles, intervening between 
the liquid and the copper, reduce the chemical action and also 
present a high resistance to the flow of the current, thus 
doubly interfering with the working of the cell. When they 
stop the current entirely, the cell is said to be polarized. 

27. A cell may be depolarized by mechanical action : caus- 
ing the bubbles to rise to the surface ; or by adding a chemical 
that absorbs the hydrogen gas ; or electro-chemitally : coating 
the zinc plate with a metal that will take the place of hydro- 
gen and deposit on the positive plate. — An open circuit cell is 
one in which depolarization is very slow; so the cell must be 
given time to rest between two periods of activity. They are 
used for door bells, telephones, etc., where a small current 
suffices and is in use at intervals only. — A closed circuit cell 
is one in which provision is made for constant depolarizing. 
It gives a continuous flow of current, and is used for plating., 
lighting, running small motors, and in telegraphy. 
Mechanical depolarization 

28. Mechanical depolarization could be done by constant 
stirring. In some cells the copper plate is made very rough, 



ELECTRICAL ENGINEERING 



35 



so that the bubbles will not stick to it so easily, or the positive 
plate, mostly made of carbon, is very large, the liquid con- 
sisting of sal-ammoniac. 

Chemical Depolarization 

29. Chemical depolarization is effected by adding to the 
liquid some substance that will combine with the free hydro- 
gen as quickly as it forms. Such substances are nitric acid, 
bichromate of soda or of potash, chloride of lime, dioxide of 
manganese ; the materials mostly used for the plates are zinc 
and carbon. 

30. A bunsen cell consists of a glass 
vessel containing sulphuric acid, in which 
stands a zinc cylinder, and in this a cup of 
porous earthenware containing nitric acid 
and hard carbon. The nitric acid and the 
sulphuric acid unite sufficiently through the 
porous cup to produce an electric current. 
The nitric acid is used as a depolarizer, but 
would consume the zinc very rapidly, if it 
touched it. The Bunsen cell's E. M. F. is 1*9 volts, intern, 
resist, =0*25 ohm. It is not used much, being very expensive, 
and because of the poisonous gases it produces. — The grove 
cell (fig. 8) is the same as the Bunsen, substituting platinum 
for carbon. E. M. F. = 1*95 volts, intern, resist.^ 0*15 ohm. 

Depolarization is effected in these cells as follows : The 
hydrogen liberated at the zinc plate, is oxidized in passing 
through the nitric acid, producing water and red fumes of per- 
oxide of nitrogen gas. 

31. In the edison-lalande cell the plates are made of zinc 
and compressed copper oxide. The liquid is caustic soda or 




Fig. 8. 



36 MODERN ELECTRICITY 

caustic potash dissolved in water. To protect the liquid from 
the carbonic acid in the air, it is covered with paraffine oil. 
The oxygen in the copper oxide readily combines with the 
hydrogen gas, thus efficiently preventing polarization. This 
cell is very useful for medical purposes. 

32. In a leclanche cell a porous cup containing the posi- 
tive plate or rod of carbon and small lumps of dioxide of man- 
ganese, is placed, together with a rod of zinc, in a glass vessel 
almost filled with sal-ammoniac dissolved in water. The top 
of the carbon and the inside rim of the jar are coated with 
paraffine to prevent the salts from "creeping up," and the 
porous cup is sealed with a resinous substance, leaving only 
two small holes which allow the liquid to enter the cup. This 
cell is very good for intermittent use, as for door bells and 
telephones. E. M. F. = 1*48 volts, intern, resist. = 0*4 ohm. 

33. A plunge battery consists of a set of cells made of 
zinc, carbon and a bichromate dissolved in sulphuric acid. It 
is so arranged that the plates may be lifted out of the liquid 
when not used, — because the liquid destroys the zinc very 
rapidly. The liquid is prepared by dissolving the crushed bi- 
chromate (6 parts) in boiling water (90 parts), cooling it 
and adding sulphuric acid (12 parts). This battery is used 
to run small motors, ignite the gas in gas engines, etc. It 
gives a large current. 

Electrochemical depolarization 

34. Where continuous service is required, Daniell's cells 
and Gravity ceils are generally used. Daniell's cell has a 
zinc plate immersed in dilute sulphuric acid, and, in a porous 
cup, a copper plate immersed in a depolarizing solution of 



ELECTRICAL ENGINEERING 



37 



blue vitriol (copper sulphate). The acid eats into the zin< 
forming sulphate of zinc and liberating hydrogen, which com 
bines with the copper sulphate, taking from it copper and de- 
positing it on the copper plate, which is in this way kept bright 
and in good condition. It is necessary to keep up the full 
strength of the copper sulphate by adding crystals of blue 
vitriol from time to time. The E. M. F. of this cell is 1-08 
volts, intern, resist. = 061 ohm. 

35. A gravity cell (see fig. 9) is made of the same 
materials as the Daniell's cell, but the arrangement is differ- 
ent. The blue vitriol, being much heavier than the well 
diluted sulphuric acid, is put in the bottom of the jar with the 
copper plate and the crystals. Then water 
is poured on very gently, so it will float on 
top, and the zinc is suspended in it. By 
pouring a few drops of sulphuric acid into 
the water, the cell will at once work. The 
two liquids mix gradually by diffusion, 
unless there is a constant current. If the 
copper sulphate reaches the zinc, it deposits 
on it oxide of copper, making it unfit for 
service, until cleaned. It is very good in a 
closed circuit battery, there being absolutely no polarization 
but not for intermittent work. The E. M. F. is 1-07 volts. 

36. A dry battery cell, or dry cell, has zinc and carbon 
electrodes of various shapes, separated by a sal-ammoniac or 
acid paste. Generally a zinc cup is used for the outer shell, 
the carbon being in the cup, surrounded by the paste, and the 
whole sealed with a resinous substance. The E. M. F. of dif- 
ferent types differs, the average being 1*5 volts. 




Fig. 9. 



38 



MODERN ELECTRICITY 
CONSTANTS OF CELLS. 



Name of Cell. 



Bunsen . . . 

Zinc (Zn) 
Carbon (C) 

Clark (Standard) . . . . 
A., zinc (Zn) 
JC. 9 mercury (Hg) 

Daniell (Meidinger, etc.) 
A , zinc (Zn) 
K., copper (Cu) 

Grove 

A., zinc (Zn) 
K., Platinum (Pt) 

Dry cells 

A., zinc (Zn) 
A"., carbon (C) 

Leclanche 

A., zinc (Zn) 
A'., carbon (C) 

Smee 

A., zinc (Zn) 

K. platinized silver ( Ag) 



Exciting 
solution. 



sulphuric 
acid 
+H 2 
Zn SO* 



Zn S0 4 
H 2 S0 4 
various 
N H 4 C1 
H 2 S0 4 



Manner 
of depo- 
larization 



chemical 



electro- 
chemical 

electro- 
chemical 

chemical 



chem. or 
electro- 
chemical 
chemical 



median 
ical. 



Depo- 
larizer. 



Nitric 
acid 

Hg 2 S0 4 

Cu S0 4 
HNO3 
various 
Mn 2 

none 



Approxim. 

E. M. F. 

Volts. 



I'9 

1 43 
1 079 

1-95 



1-46 
various 

1-48 



1-0-0-59 



Approx. int. 

resistance. 

Ohms. 



o 05-0-25 



various 



061 



0-15 



0-2 



0-3-0-5 



o-i 



Zinc and its consumption 

37. Electrical energy is furnished in all these different bat- 
teries at the expense of a consumption of zinc. But zinc is 
too expensive to use a battery for furnishing current of great 
magnitude, as in electric lighting. It is much cheaper to 
produce electricity by running a dynamo with a steam engine. 

Pure zinc is hard to get, and the impurities contained 
in the common commercial article cause the so-called local 
action, which is an eating away of the zinc in the impure 
spots, which form small local cells with the surrounding 



ELECTRICAL ENGINEERING 39 

pure zinc. To prevent this local action, the surface of the zinc 
plate may be amalgamated with mercury. After cleaning the 
surface of the zinc by dipping it in a weak acid solution, a 
little mercury is rubbed onto it. The mercury makes a pasty, 
shining amalgam with the pure zinc, covering up the impuri- 
ties, with which the mercury does not mix. The pure zinc in 
the amalgam is consumed by the acid, but the mercury keeps 
forming an amalgam with the pure zinc below, and thus the 
plate is kept in working order. The mercury may be addec 
when the zinc is being cast, with results equally good. 

The quantity of zinc consumed in a cell depends on the 
amount of electricity that passes through it. The quantity con- 
sumed, when one coulomb of electricity passes through a cell, 
is called the electrochemical equivalent of zinc. (See § 49). 

Secondary Battery or Accumulator 

38. A "Secondary Battery" or "Accumulator" is an appara- 
tus by which energy can be accumulated and stored in form 
of chemical work. The secondary battery does not develop any 
energy, but it converts the electric energy supplied to it by a 
dynamo or by primary batteries into chemical work,, which 
may be stored up in this state, and then used at convenience, 
by again converting the stored up chemical work into elec- 
trical energy. The Leyden jar, which can be charged and 
discharged, is a simple accumulator. 

When the liquid of a cell is saturated with the dissolved zinc 
(zinc sulphate), the zinc may be deposited again on the zinc 
plate by sending an electric current, generated by another cell 
or a dynamo, from the copper plate through the liquid to the 
zinc plate. The zinc thus re-deposited is then, of course, 
ready to be dissolved again by the electro-chemical action of 



40 



MODERN ELECTRICITY 



its own cell. The process of re-depositing the dissolved zinc 
by means of an electric current is called charging the 
storage battery, and the using of the stored up energy is 
called discharging. Of course, it is not possible to expend the 
same amount of energy in discharging, as was used in charg- 
ing ; there is considerable loss. 

39. The common storage cell (see fig. 10) is made up 
of two lead plates, or two sets of lead plates, corrugated or 
perforated (grids), each set fastened together so that the 
plates of one set fit in between those of the other, but do not 
touch them. They are immersed in dilute sulphuric acid. 
Such a cell does not generate any electric current of its own, 
it simply delivers the current received and stored. When this 
cell enters into the circuit of an electric current, there is at 
once a very lively chemical action. The plates through which 
the current enters the cell, (anode) receive a coating of lead 
oxide, (peroxide of lead), while the surface of the other set 
of plates (cathode) turns gray and spongy. As soon as the 
anode plates are completely covered with 
the red peroxide of lead, the cell is 
charged to its capacity, and it must be 
taken out of the circuit of the battery or 
dynamo, or the plates may bend, which 
would spoil the cell. 

When the poles of such a charged cell 
are connected, a current flows immediately 
from the gray plates through the liquid 
toward the reddish ones, that is in the 
direction opposite to that during the charging process ; and the 
chemical action is also the opposite, undoing the work of the 




000000 
000000 
000000 
000000 
000000 

800000 




Fig. 10. 



ELECTRICAL ENGINEERING 



41 



charging process ; the oxide of lead changes to sulphate of 
lead, and the spongy lead on the other plates also changes to 
sulphate of lead. The current continues until the surface on 
all the plates is well changed to sulphate of lead, then the 
action ceases, as two different metals are always required to 
generate an electric current. The discharge is then complete, 
and the cell is ready to be charged again, and so on. Storage 
batteries are called secondary batteries, as distinguished 
from the primary batteries, by means of which they may 
be charged. 

40. It is safe to say that, on account of the loss of energy 
incident to imperfect material and imperfect chemical action, 
a storage battery in actual service will yield only one half ot 
the voltage with which it was charged. The pressure obtain- 
able is about 2*2 volts at the start, and gradually drops to 1-8 
volts, below which point it should not be allowed to go. It 
must never be allowed to become completely discharged, as 
this would result in serious damage to the plates. Nor should 
it remain in the discharged state for any length of time, as the 
positive plates would sulphate ; it is best to charge the cell un- 
til the positive plates assume a deep brownish red color and 
the liquid effervesces violently ; in this state the battery may 
stand idle without sulphating for about two months, adding 
water enough occasionally to keep the plates covered about 
one half of one inch above the tops. 

41. The method described above is called the corroding 
or forming or plante method, being rather slow. A quicker 
way is by the pasting or faure process, in which a paste of 
red oxide (minium) moistened with sulphuric acid is filled 
into the perforations of the positive plates, and a paste of yel~ 



42 



MODERN ELECTRICITY 




low oxide of lead (litharge) is put on the negative plate. 
During the charging process, the minium changes to peroxide 
of lead, and the litharge to lead. Or both plates may be 
pasted with sulphate of lead moistened with sulphuric acid. 

riaking a storage battery 

42. A storage battery that would supply 40 incandescent 
lamps of 16 candle power (c. p.) for 5 hours, or 5 lamps for 
40 hours, etc., can be made as follows : 

Assuming that it takes \ ampere per 
lamp, there will be required 40 X £ X 5 
= 100 ampere hours. Procure a quantity of 
lead tape one-64th inch thick by f inch 
wide, known to the trade as torpedo lead, 
and a quantity of f X \ inch strip lead called 
chemical or desilverized lead. If the strips 
cannot be obtained, get about 10 pounds of 

W sheet lead, \ inch thick and cut into strips 

.. WW^ l f inch wide. With these g-X \ inch strips 
proceed to make seven frames ; size inside 
7X6 inches, molding them around a 7 X 6 
block of wood, so as to have them all alike. 
(See fig. 11.) Insert a § strip between the 
projecting ends (lugs), and solder firmly 
together with a blowpipe and rosin. 
Now cut off a number of torpedo lead strips 6 inches long, 
and as many of 8 inches ; corrugate the 8 inch strips and fit 
them all into the seven frames the 6 inch way, as in fig. 12. 
Fuse the ends, so the strips will not fall out. Then paste 
four of the frames with a mixture of 3£ pounds of yellow lead 
and 1 part sulphuric acid and 10 parts water. These are the 



Fig. 11. 



AVAVAVAVAVAN 



/AVAVAWAVAN 



/aVaVaVaWaN 



/aVaWaWaN 



/aVaVaVaWaN 



AWVVWAN 



Fig. 12. 



ELECTRICAL ENGINEERING 



43 



13. 



negative plates. Then fill the other three frames with a com- 
position of 2£ pounds of red lead mixed with 1 part sulphuric 
acid and 10 parts water. These are the positive plates. 

Now take sheets of card board about three- 16ths of an inch 
in thickness, soak well in silicate of soda, and let thoroughly 
dry. When ready, lay a negative plate on its side ; place on 
top a sheet of prepared cardboard, then a positive plate with 
the lug opposite to the negative lug. then a sheet, then a nega- 
tive, and so on until all are laid, then tie up tightly with string. 
Fuse a heavy strip of lead, (see fig. 13), 
called binding or head strips, across the 3 1 =»-. J 
positive plates, and another across the 4 
negative plates (see fig. 14). Put them in 
a glass jar or asphalt coated, tight box, that 
will hold acid. * The liquid and the manner 
of preparing it, has been described. It is 
well to add about two ounces of bicarbonate 
of soda Connect the positive bar with wire 
to the positive wire of dynamo, and the 
negative bar with the negative wire of dynamo, and pass a 
current of 10 amperes into the storage battery for 48 hours 
until the solution in battery gasses or boils well. This battery 
when charged will deliver 100 ampere hours at 2 volts 
pressure. 

43. The modern Edison battery has a shell of sheet steel ; 
the plates are firmly set in between hard rubber, and consist 
of thin sheet steel frames with slits in which iron oxide 
(positive) and of nickel hydrate ( negative ) have been 
pressed hydraulically, and covered with perforated steel 
I- is. Each cell has twenty-four plates, 9£ X 4f inches, 




Fig. 14. 



44 MODERN ELECTRICITY 

0-1 inch thick. The electrolyte is caustic potash. All the 
attention it needs is replacing the water that may have evapo- 
rated. It can be discharged at the rate of 200 amperes with- 
out damage. It may be run down to without harm. It gives 
out one H. P. for each 53*3 pounds of weight. The chemical 
charge consists in the transference of oxygen to the nickel side 
when charging, and to the iron side when discharging. 

Charging a secondary battery 

44. By a battery. The primary current causes an opposing 
E. M. F. in the secondary cells, therefore the source furnish- 
ing the primary current must have a higher E. M. F. than the 
secondary cell. In order to charge an accumulator of 12 cells 
of 2-2 volts each, joined in series, the E. M. F. of the source 
must be more than 12X2-2. However, if the source pos- 
sesses only 3 volts, the secondary cells might be joined in 
parallel, so as to represent one large cell. But it is best to 
use currents of moderate strength, and one large cell works 
better than several small ones joined up in parallel, because it 
is impossible to have the cells exactly alike, and those sub- 
jected to the stronger currents are likely to be damaged. 

By a dynamo. The secondary cells are best arranged 
in series, The process of charging should be slow. Dynamos 
with permanent steel magnets are used, as they do not change 
their poles. The machine should be shunt-wound, because if 
the whole circuit were in series, it might happen that the 
E. M. F. of the secondary battery became stronger than that 
of the source, and the current would be reversed, injuring the 
machine. In using a shunt-wound dynamo two circuits are 
connected with the brushes of the commutator: one circuit 
has the sec. battery, the other the field coils and a rheostat. 



ELECTRICAL ENGINEERING 



45 



The two currents are inversely proportional to their resistances, 
therefore, the resistance can be regulated by means of the 
rheostat. Great care, however, is needed, to avoid a heavier 
E. M. F. in the secondary battery than in the generator. Hospi- 
taller's charger breaks the circuit as soon as the machine 
current decreases beyond a certain point, and connect again, 
when the machine current has regained the required strength. 
Accumulator switch-boards are used for the same purpose. 

Arrangement of cells in batteries 

44. A broad stream of water might run a number of mill- 
wheels at the same point, the wheels being erected abreast on 
a straight line across the 

current. If the same num- -©^©-0-^-0— ©* 
ber of mill-wheels are to 
be turned by a small stream 
of water, they must be 
placed along the current, 
one below the other. In 
the first case we have a 
large quantity of water and 
a small fall ; in the second 
case a small quantity of 
water and a large fall. 

In the same way, the 
cells of a battery may be connected so as to generate a 
large current at low pressure, or a small current at high 
pressure. If the positive pole of one cell is always con- 
nected with the negative pole of the next (see fig. 15 A) 
the cells are said to be connected in series (as in a Voltaic 
pile), and the more cells there are, the greater will be 



(j) B (^) ($ (f) (p (y) 





Fig. 15. 



46 MODERN ELECTRICITY 

the E. M. F. Six cells of 1*5 volts and 4 amperes each 
would give 9 volts and 4 amperes, The current would not 
be stronger than that of a single cell. 

EXAMPLE 2. 

The E. M. F. of a single cell is 1 volt; its internal resist- 
ance is 2*4 ohms, and the external 3 ohms. What is the 
strength of the current ? (See foot note.*) 

1 -r- (2-4 + 3) = 1 h- 5-4 = 0* 1 85 ampere. Ans. 

EXAMPLE 3. 
The E. M. F. of each of 6 cells connected in series is 1-5 
volts ; the internal resistance of each is 2 ohms ; the external 
resistance 4 ohms. What is the strength of the current? 

l-5X6-[(2X6) + 4]=^ = 0-56 ampere. Ans. 

On the other hand, if all the positive poles of the cells are 
connected together, and the negatives together, in parallel 
or for quantity, (Fig. 15 B) the voltage is the same as in the 
single cell, but the strength of the current equals the sum of 
all the amperes delivered by each cell, because the internal 
resistance is reduced in direct proportion to the number cf 
cells, owing to the increased number of paths. It is exactly 
as if the cells had been replaced by one large cell, the area 
of whose plate equaled the sum of the areas of the several 
small plates. This is why the lead plates in a storage battery 
are connected in parallel. 

If 2 cells are connected, each of 1-5 volts and 4 amperes, 
in parallel, and three of such groups in series (Fig. 15 C), 
then the E M. F. of one group =1 -5 volts, and the intensity of 
the current 1=2X4=8 amperes, and the E.M.F. of the whole 

* Current = E. M. F. divided by resistance. See §51. 



ELECTRICAL ENGINEERING 



47 



battery, E= 1-5X 3 = 45 volts and I = 8 amperes. If these 
these cells are joined in 2 groups in series, each group of 3 
cells in parallel, (Fig. 15 D), then the E. M. F. of one group 
E = 1 -5 volts, and 1 = 3X4 = 12 amperes, and the E of the 
whole battery, E =2X1-5=3 volts and 1 = 12 amperes. 

EXAMPLE 4. 

6 cells are joined in parallel; E. M. F. of each cell 1-5 
volts, internal resistance 2 ohms, external -5. What is the 
strength of the current ? 

It is equal to the E. M. F. of a single cell (1*5) divided by 
the sum of the external resistance (-5) plus the interna* 
resistance (2) divided by the number of cells (6). 

^ ■ = — =1.8 amperes. Ans. 



+ '5 



•83 




Fig. 16. 



Fig. 17. 



Fig. 16 represents the cells connected in series multiple. 
Fig. 17 represents cells connected in series multiple in series. 
Any such combination (of both series and parallel) as in fig. 
1 5 C, D, and figs. 1 6 and 1 7 is said to be connected in series 
multiple. 

By the arrangement of fig. 16, the internal resistance of 
the battery is reduced directly in proportion to the number of 



48 MODERN ELECTRICITY 

series; the E. M. F. of the battery and the internal resistance 
of each series are both increased in proportion to the number 
of cells in each series. In consequence, the current will equal 
the E. M. F. of a single cell multiplied by the number of cells 
in each series, divided by the internal resistance of a cell 
times the number of cells in series, divided by (the number of 
series plus the external resistance of the circuit). 

EXAMPLE 5. 
A battery of 6 cells is arranged 3 in series and 2 in parallel. 
The E. M. F. of one cell is 1*5 volts, and its internal resist- 
ance 5 ohms; external resistance is 2 ohms. What is the 
strength of the current? 

3X 1-5 4-5 

3X^^275= 1-6 amperes. Ans. 



EXAMPLE 6. 

Find the current of a battery of 24 cells arranged 8 in 
series and 3 in parallel. The E. M. F. of one cell is 1.5 volts, 
and its internal resistance -5 ohm ; external resist, is 6 ohms. 

8X1-5 12 36 1A , f 

8X05- == 7T = 22 =1 ' 64 amp ' ( a PP rox -> 
~^ + 6 

EXAMPLE 7. 
A battery arranged in series with the E. M. F. of each cell 
2-5 volts, and an internal resistance of *5 ohm, drives a current 
of 3 amperes through a circuit of 9 ohm resistance. How 
many cells are there ? 

We assume x to be the number of cells. 

'' 3 = ^V^-- 3(-5* + 9)=2-5* 



xXr+R' Sx + 9 

1-5* + 27 =2-5x; x = 27 cells. Ans. 



ELECTRICAL ENGINEERING 49 

EXAMPLE 8. 

A battery arranged in parallel, with E. M. F. of each cell 4 
volts, internal resistance 5 ohms, external resistance 1 ohm, 
drives a current of 2 amperes. How many cells? 

4 4 5 
2 = - ; -= -+ 1 ; multiplying by x t we get 2 x = 5 + x; 

-+1 

x x = 5 cells. Ans. 

In order to have a steady current of the greatest service- 
ableness, the cells should be so arranged that the internal 
resistance will equal the external. 

EXAMPLE 9. 

125 cells, with a resistance of 1 ohm per cell, are to be so 
arranged as to send the maximum current through an external 
resistance of 5 ohms. 

To find the inner resistance, we multiply 1 (ohm) by the 
number of cells in series (*), divided by the number in 
parallel (y), and make this quotient = 5. 

^^ = 5 and xX y = 125 

y 

x = 5 y and 5 yX y = 125 
5 /= 125 ^ 125 =25 

y = 5 in parallel. y = 25 in series. Ans. 

RULE 5. — The efficiency of a battery, in percentage, equals 
the external resistance, multiplied by 100, and divided by the 
sum of the external and internal resistances. 

EXAMPLE 10. 
A battery of 40 cells ; external resistance 16 ohms; inter- 
nal resistance of each cell -5 ohm. What is the efficiency? 
16 X 100 1600 AA 

lHWx~5) = l6- = 44 ' 4perCent AnS ' 



50 MODERN ELECTRICITY 

Electrolysis 

45. electrolytes, as explained in §25, are solutions of 
acids or salts of the metals, in which electrolysis, electro- 
chemical decomposition, takes place when a current flows 
through them. The plate at which the current enters the cell, 
is called the positive electrode, or anode ; the other plate 
is termed the negative electrode, or cathode. The pro- 
ducts of electrolysis are called ions (anions and kations). A 
salt of a metal (as sulphate, chloride, nitrate, or carbonate 
of copper) is the product of the action of an acid o*\ the 
metal ; carbonic acid acting on copper produces carbonate of 
copper; sulphuric acid acting on copper produces sulphate of 
copper. Now, sulphuric acid consists of its acid radical 
(sulphur and oxygen), combined with hydrogen. But the 
acid radical has a greater affinity for copper than for hydro- 
gen, especially when heated,* and as soon as a piece of 
copper is placed in the acid, the acid radical enters into a 
chemical combination with it, forming sulphate of copper, 
while the hydrogen is liberated. The sulphate of copper stays 
in the liquid, unless it is crystallized out in the form of blue 
crystal-like lumps. But if this liquid containing sulphate of 
copper is used as the electrolyte for two copper plates con- 
nected with a battery, the electric current at once decomposes 
the sulphate into its two parts, the acid radical and metallic 
copper, and deposits the copper on the cathode. The acid 
radical liberated returns to the work of attacking the copper 
of the anode, and so on. The anode will gradually be dissolved, 
while the cathode will increase in size. (See more about this 
in the chapter on Plating.) 

* Sulphuric acid has a great affinity for water, and unites with it readily 
in any proportion, evolving at the same time gieat heat. 



ELECTRICAL ENGINEERING 51 

46. On the same principle it is possible to electrolyze 
the salts of other metals, and even liquids that hold no salts 
in solution. If, for instance, two platinum plates connected 
with a battery are placed in an electrolyte containing sulphate 
of copper, the copper is deposited on the cathode, but —the 
acid radical having no affinity for platinum, does not attack it. 
It attacks, therefore, that within its reach for which it has the 
greatest affinity, which in this case is the water in the solution. 
It combines chemically with tne hydrogen in the water, form- 
ing again sulphuric acid, and liberating the oxygen, which 
collects in bubbles on the anode and escapes. After all the 
copper dissolved in the electrolyte has been deposited on the 
cathode, the chemical action will be limited to the decom- 
position of the water, the hydrogen bubbles appearing at the 
cathode and the oxygen bubbles on the anode. The general 
principle, of vast industrial importance, of chemical action in 
an electrolytic cell is : 

RULE 6. — The acid radical, or its equivalent in oxygen, 
flows against the direction of the electric current toward the 
anode ; the metal part, or its equivalent in hydrogen, flows with 
the electric current towards the cathode. 

Chemical equivalents 

47. It is characteristic of all primary cells, that oxidation 
takes places on one plate, and that there is no action what- 
ever on the other plate, the hydrogen remaining in its gaseous 
state. The hydrogen, easily measured, is therefore taken as 
the unit. Hydrogen is released in a definite, invariable ratio 
to the amount of zinc dissolved : for every atom of zinc con- 
verted into sulphate of zinc, two atoms of hydrogen are lib- 
erated ; but an atom of zinc weighs 65 times as much as an 



52 MODERN ELECTRICITY 

atom of hydrogen, so that the weight of zinc dissolved will be 
32*5 times as much as that of the hydrogen. This is meant 
by the expression : "the chemical equivalent of zinc is 32-5," 
taking that of hydrogen as the unit (1). A quantity of acid 
that will just dissolve 325 grammes of zinc, will also just 
dissolve 29-3 grammes of nickel. These values, given in the 
table below, are at the same time the rates at which the metals 
enter into chemical combinations. This is easily understood by 
the action of the voltameter (§50), in which water is 
dissolved into oxygen and hydrogen : the two elements will 
certainly combine again into water in the same proportions. 
It is, furthermore, true that the power expended in making a 
given amount of chemical change, is equal to the power 
necessary to undo this change (see §83), making due allow- 
ance for unavoidable losses. 

Electrochemical equivalents 

48. After the chemical equivalents in weight have been 
determined for the several metals, etc., used in electrolysis, 
by experiments, it is easy to find the electro-chemical 
equivalents by multiplying together the weight of the hydrogen 
liberated by one coulomb of electricity and the chemical 
equivalent of each of the other elements or substances. For 
instance, to find the electro-chemical equivalent of nickel, we 
multiply -010384 X 29-3 = -30425. On the other hand, the 
electro-chemical equivalent in milligrammes per coulomb, of 
any metal, divided by the electro-chemical equivalent of 
hydrogen (-01C384) gives the chemical equivalent of the 
metal. 

The international ampere adopted by the Electrical 
Congress in Chicago, 1893, is a steady current which 



ELECTRICAL ENGINEERING 



53 



deposits silver at the rate of -001118 grammes (or 1*118 
milligrammes) per second (or 4*025 gr. per hour) from a 
solution of silver nitrate in water, of a fixed strength. The 
following table gives the rates for other metals and sub- 
stances : 

TABLE OF ELECTRO-CHEMICAL EQUIVALENTS. 



Ions. 



H-Aluminum , 

+Copper (cupric)* . . . . 
+Copper (cuprous) 

■f Gold 

+Hydrogen 

+Iron (ferrous) 

+Iron (ferric) 

+Lead 

-f Mercury (mercuric) . . 
+Mercury (mercurous) 

+Nickel 

—Nitrogen 



-Oxygen 
+Potassium . . . . 

+Silver 

-KTin (stannic) . 
-f-Tin (stannous), 
+Zinc 



Symbol 

and 
Valency 



Al 3 

Cu 2 

Cui 

Au 3 

Hz 

Fe 2 

Fe 3 

Pb 2 

Hg 2 

Hgx 

Ni 2 

N 3 

o 2 

Ki 

Agi 
Sn 4 
Sn 2 
Zn 2 



Atomic 
Weight. 



27*3 
63*18 
6 3 -l8 
196-2 

I 

55*9 

55*9 
206 '4 

199-8 
199-8 
58-6 
14*01 
15-96 

39*03 
107*67 

117-8 

117-8 

64-9 



Chemical 
Equiva- 
lent 
in weight. 



9*01 

31*59 
63-18 

65*4 

1 

18-6 

27-9 

103-2 

99*9 
199-8 

29*3 
4-67 

7' 9 8 

39*03 
107*67 

29*45 

58-9 

32*45 



Electro- 
chemical 
Equival'nts 
mg. p. c t 



O.0936 
O.3290 
O.6588 
O.6818 
O.IO39 

o. 1932 

O.2898 
I. 073 I 
LO363 
2.0727 
O.3044 
O.O488 
O.083I 

o • 4°5 l 

1.1183 

0.3083 

0.6166 

0.3385 



Deposits in 


grammes 


per Ampere 


hour. 


0*3370 


I 1*1819 


2-4458 


0*0374 


0*6955 


1*0433 


3*8595 


3*73^2 


7*4725 


1-0958 


0-1758 


0*2992 


1-4584 


4-026 


1-0958 


2*1953 


1-2118 



-f- means electro-positive, — electro-negative. 

* Some metals have two chemical equivalents, for two classes of compounds 
one being a multiple of the other ( l / 2 or %)> 

t Milligrammes per coulomb. Note that the electro-chemical equivalents are 
given in milligrammes, not grammes. (= in grammes p. c. X 1000). 



Faraday's Laws 

49. On the basis of the above named general principle 
(§ 46) and facts (§§ 47, 48), Faraday succeeded in estab- 
lishing, by his experiments, the following two laws : 



54 



MODERN ELECTRICITY 



RULE 7. — The quantity of the electrolyte decomposed by an 
electric current depends on the number of coulombs that pass 
through it. The size of the electrodes and the voltage are of 
no consequence. 

RULE 8. — Equal quantities of electricity passing through 
different electrolytes, decompose equivalent quantities of the 
electrolytes, that is to say, the chemical change worked by 
the passing of one coulomb, depends on the equivalent weights 
of the elements in the electrolyte. 

Water voltameter 

50. Perfectly pure water is a non-conductor and is, therefore, 
not decomposed by electrolysis, but by the addition of some 
sulphuric acid this condition is changed, and after the current 
has decomposed the acid, the acid ions in turn 
become the means of decomposing the water 
into its two elements, hydrogen and oxygen. 
The above table shows that one coulomb of 
electricity liberates almost 8 times more oxygen 
than hydrogen ( in weight ). In the diagram 
(fig. 18) of a water voltameter, the three con- 
necting tubes are filled with slightly acidulated 
water and A and B emptied of air through the 
When the platinum plates in A and B are con- 
nected with the battery D, there appears very soon hydrogen 
in tube B and oxygen in tube A, in the proportion of 1 to 8 
by weight. But a given weight of oxygen is of so much 
smaller volume than the same weight of hydrogen, that the 
water in the oxygen tube will be pressed down only about half 
as far as that in the hydrogen tube. From the amount of 




ELECTRICAL ENGINEERING 55 

gases collected and their electro-chemical equivalents the 
strength of the current can be calculated : The number of 
coulombs flowing per second equals the amperes of current. 

Questions and Answers. 

Q. How many kinds of depolarization are there ? 

A. Three: mechanical, chemical, and electro-chemical. 

Q. Which kind is used in the bichromate cell ? 

A. The chemical. 

Q. Describe a bichromate cell and its working? 

A. Zinc and carbon plates in dilute sulphuric acid and bi- 
chromate of potash. The zinc should be taken out, when the 
cell is not used. It gives a large electro-motive force ( 1 *95 
volts), is used as a closed circuit cell, but is not constant. 

Q. How is the liquid mixed ? 

A. Add 5 ounces of sulphuric acid slowly to 3 pints of cold 
water; when cooled, add 6 ounces of pulverized bichromate of 
potash or soda, mixing well. 

Q. What is a silver chloride cell ? 

A. It consists of a zinc plate and a silver plate upon which 
silver chloride has been cast, in sal ammoniac or ammonium 
chloride, the silver chloride acting as depolarizer. 

Q. What is a crowfoot ? 

A. The zinc in a gravity cell is so named from its shape. 

Q. Does a large cell give a higher pressure and a larger 
current than a small one ? 

A. It gives a larger current but not a higher pressure. 

Q. Does a plunge battery give a large current? 

A. Yes, as many as 30 amperes have been obtained from 
a single cell. 



56 MODERN ELECTRICITY 

Q. How could a powerful single cell plurge battery be made 
for experimental purposes and obtain from 25 to 28 amperes, 
and the glass jar not to be over five inches square ? 

A. Fasten a number of carbon plates close to the sides of 
zinc plates, and plunge into tank containing a solution of one- 
half pint sulphuric acid, one quart water, and one-fourth 
pound bichromate of potash. Arrange the plates so that 
they can all be raised up out of the solution at once when 
not in use, 

Q How is evaporation in a storage battery prevented ? 

A. If the cell is covered up with a glass plate, the vapor 
will condense on it and fall back in drops. 

Q. What points are to be observed about storage batteries? 

A They must be kept clean, and the connections should 
be tight, as any dirt would increase resistance, reducing the 
efficiency of the battery. 

Q. What is the rule for finding the efficiency of a 

BATTERY ? 

A. Divide the resistance of the external circuit, by the 
resistance of the external circuit plus the internal resistance, 
and multiply by 100. This gives the percentage of efficiency 

Q. Give an example. 

A. In a battery of 12 cells, the external resistance being 
20 ohms, and the internal resistance of each cell -2 ohms, 

20 20 X 100 

We haVe 20 + (12X-2) X 10 ° = ^2^ = 89 Per Cent " 

Q. What is meant by short-circuiting a cell. 

A. It means connecting the two terminals or external poles 
by a short wire, instead of connecting it with a system of 
wires, bells or other devices. 



ELECTRICAL ENGINEERING 57 

Q. If we have several voltameters of different sizes con- 
nected in series, will the chemical action in them vary in 
quantity ? 

A. No, it will be the same in each cell, because the same 
amount of current flows through them all. 

Q. If ten cells, each with a pressure of 9-10ths of a volt, 
are connected in series, what will be the total pressure ? 

A. Nine volts. 

Q. How do you calculate the amount of any metal sepa- 
rated from the electrolyte, when the amount of silver sepa- 
rated under the same circumstances is known ? 

A. Multiply the weight of the silver by the ratio of the 
equivalent weight of the other metal to that of silver. 

Q. Give an example. 

A. Assuming that 12 ounces of silver have been separated, 
then the amount of nickel separated under the same circum- 

29 3 

stances would be 12X— ^z- =3*26 ounces. (See table on 

page 53.) 

Q. Is it known how the chemical decomposition in an 
electrolytic cell takes place? 

A. Not with certainty. The theory Is that the molecules 
break up into their atoms, and that one class of these atoms 
have a strong affinity for one of the electrodes, and flow 
toward it, repelling the other kind towards the other electrode. 

Q. What is the meaning of P. D. ? 

A, Potential difference. 

Q. What is the meaning of C. G. S. ? 

A. It means the centimeter-gramme-second system of 
electrical units, almost universally employed by electricians. 



CHAPTER IV. — Intensity of Electric Currents 

Ohm's law 

51. In the same way in which two pipes of equal size, 
and under the same pressure, may not deliver the same 
quantity of water, owing to greater roughness of the inner 
surface in one of them, so the electric current's flow depends 
on the material and size of the conductor. But while in the 
case of a water pipe the friction is only on the surface of the 
water column, in the case of the electric conductor the resist- 
ance is in the whole cross-section, and, besides the length, 
the temperature is of consequence. The law for measuring 
is the same in the two cases. 

RULE 9. — The flow equals the pressure divided by the 
resistance. 

The German scientist Ohm was the first to make this appli- 
cation of the general law : The result equals the effort divided 
by the resistance, and the rule is, therefore, properly named 

B 
after him. In the formula I = t >1 expressive of Ohm's Law. 

IX 

I, E, R, mean intensity (current), electromotive force (press- 

B 
ure), resistance, From this formula we derive also: R = y 

and E = IXR, which is easily understood by substituting 
proper figures : 7 = 42^-6 ; 6 X 42 -*- 7 ; 42 = 6 X 7. 

EXAMPLE 10A. 

a. Through a wire of 20 ohms resistance, at a pressure of 
100 volts, a current of 5 amperes will flow. 

b. A conductor using 3 amperes at 60 volts pressure, has a 
resistance of 20 ohms. 

58 



ELECTRICAL ENGINEERING 59 

c. A lamp filament using 4 amperes at a resistance of 100 
ohms requires 400 volts to make it properly incandescent. 

52. The term "total resistance" means, in the case of a 
battery, the sum of the internal resistances in each cell added 
to that of the conductor. If there are 6 cells, each with a 
pressure of 1*5 volts and an internal resistance of 2 ohms, 
connected in series with an external circuit of 3 ohms resist- 
ance , then the total resistance equals (6X2)+3= 15, and 
the pressure is 6X1*5 volts. Therefore the current is 

, E 6X1-5 9 3 

/= ^ = (6X2)+3 = T5 = 5^ ' 6ampere ' 

Conductance 

53. As stated in § 8, the metals vary greatly in con- 
ductance.* Pure silver and copper, showing the least resist- 
ance to the electric current, have been taken as the standards 
for conductance, being marked 100, and the other metals in 
percentage. (For exact values see p. 62.) 

Pure silver, 100 Platinum, . 17 Lead, ... 8 

Pure copper, 100 Wrought iron, 16 German silver, 7 

Gold, . . 76 Nickel, . . 12 Cast iron, . . 3 

Aluminum, 54 Tin, . 12 Mercury, . .1.6 
Zinc, . . 28 

These figures refer to wires of equal lengths and cross 
sections. They ard subject to changes, dependent on the 
quality of the metal, due to its origin or the process of manu- 
facturing, or other conditions. 

* Conductance is the reverse of resistance. Conductance = : * 

resistance 

Conductivity or Specific Conductance is the conductance of a prism 1 cm. long 
and 1 sq. cm. in cross-section. 

Resistivity or Specific Resistance is the resistance of a prism 1 cm. long and 
1 sq. cm. in cross-section. 



60 MODERN ELECTRICITY 

Standard of resistance 

54. The conductance of a conductor increases with its cross 
section; its resistance increases with its length. Applied to 
cylindrical wires of equal length, this means that their con- 
ducting power is directly proportional to the squares of their 
diameters, and their resistance is inversely proportional to the 
squares of their diameters. A wire of one centimeter thickness 
has only \ of the resistance of a wire £ centimeter thick. 
At the Electrical Congress held in Chicago during the world's 
fair, 1893, the international ohm was established as the 
unit of resistance. It is the resistance of a column of pure 
mercury, 106*3 centimeters long, of a uniform cross section 
of one square millimeter at the temperature of melting ice. 
Such a column contains 14*452 1 grammes of mercury. As 
such mercury columns are inconvenient to handle, so-called 
resistance coils, of German silver or other high resistance 
wire, adjusted, by means of the mercury column, to any 
desired number of ohms, are used for measuring resistance in 
practical service. (See Rheostat, Chap. VII.) 

Temperature coefficient 

55. In §51 it was said that the temperature had great 
effect on resistance. In most metals it increases with the 
rising temperature, while in bad conductors it decreases greatly 
with increasing heat. Glass is a conductor when at red heat, 
and the carbon in the incandescent lamp has only about 
half the resistance when incandescent, that it has when cold. 
In general, it may be said that pure metals change 1 per cent 
in resistance for every 4-5 degrees Fahrenheit, up or down the 
scale, or for every 2*5 degrees centigrade, or, in other words, 
four tenths of one per cent for every degree centigrade, or 22 



ELECTRICAL ENGINEERING 61 

hundredths for every degree Fahrenheit. This is called the 
temperature coefficient of pure metals. For German 
silver the value is about one tenth as much. Other alloys 
vary from the value given for German silver to 0. 

Resistance of a wire 

56. Scientists generally use a wire one centimeter long 
and of a cross section of one square centimeter in deter- 
mining its resistance, but in practice wires one foot long and 
of a cross section of one circular mil are used. Such a 
wire is called a mil foot. A circular mil is the area of a 
circle the diameter of which is one mil, which is one-thou- 
sandth of an inch. A microhm is one-millionth of an ohm. 

EXAMPLE 11. 

A wire \ inch thick has a diameter of 250 mils. Area 
of cross section equals 250X250= 62.500 circular mils; 
or, the square of the diameter in mils equals the area in 
circular mils. 

The specific resistances of ordinary wires are known; tha' 
of a mil foot of copper is about 10*5 ohms at a tempera- 
ture of 75° F. The resistance in ohms of a wire of any 
length is, therefore, the resistance of one mil foot of the wire, 
multiplied by its length in feet, and divided by the cross section 
in circular mils. 

EXAMPLE 12. 

A copper wire 5000 ft. long and 49,000 c. m. in cross sec- 
tion has a resistance = 10-5 X 5000-^-49,000 = 1 -07 ohms. 



62 



MODERN ELECTRICITY 



TABLE OF RESISTANCES. 





Specific Resistance 


Relative 
Conductance. 




MATERIAL. 


(of 1 cm. cube) 
(in microhms) 


of wire 1 

metre long, 

1 sq. mm. 

cross section 

(in ohms) 


Conductiv- 
ity com- 
pared with 
Mercury 
at 0°C 


Metals and alloys at 0° C 
Silver, pure 


I.492 
1*570 
2*077 
2*889 

8*982 
9*6 3 8 

19*63 
20*76 
94*34 

2,650,000,000 
4,860,000 
1,370,000 


0*01492 
0*01570 
0*02077 
0*02889 

0*08982 
0*0964 

0*1963 
0*2076 
Q'9434 


105 

IOO 

7 6 

54 
28 

17 
16 
12 
12 

8'3 
7-6 
i*6 

0-000,000,92 
0-000,000,83 


63-8 


Copper, pure 


55-86 
44* 06 
30*86 
16-64 
6.073 
9*685 

7374 

9*874 
5*111 
3*603 
1 *ooo 


Gold 


Aluminum 


Zinc 


Platinum 


Iron, pure 


Nickel 


Tin 


Lead 


German Silver 

Mercury 

Liquids at 18 Q C. 

Water, pure 


5% solution of H 2 S04 
30% " " 





I cm. cub. glass at 20 C has a sp. res. of 91,000,000,000,000,000,000 
and a rel. conductance of 0-000,000,000,082. 



Simple and compound circuits 

57. When a circuit consists of various parts, all of different 
resistance, but connected in series, forming a single path, 
the total resistance is the sum of all the resistances. When 
a circuit is compounded or branched, that is connected in 
parallel, each of the parallel paths must be calculated sepa- 
rately. 

EXAMPLE 13. 

If there are two branches A and B, with resistances of 5 and 
4 ohms respectively, between two common terminals, and the 
pressure is 40 volts, then the current flowing through A will 



ELECTRICAL ENGINEERING 53 

be 40^- 5 = 8 amperes, and that through B 40 ■+■ 4 = 10 
amperes, according to Ohm's law. The two currents stand 
in the proportion \ and \ (meaning that J, resp. \\ of the 
number of volts [40] will give the amperes [8, resp. 10].) 
The total current being 8+ 10=18 amperes, and the pres- 
sure being 40, the joint resistance (of the two branches) 
must be \ | = 2| ohms. The joint resistance can also be 
figured as follows : The joint conducting power is \ + \ = 
^%; the inverse* of this is %° = 2f. 

RULE 10. — In a circuit consisting of parts connected in 
parallel, the total resistance equals the inverse of the total con- 
ductance. The total conductivity equals the sum of the conduc- 
tances of the parts. 

EXAMPLE 14 

Three wires of 6, 8, and 12 ohms resistance respectively, 
are connected in parallel. Their several conductances are J-. 
|, and y 1 ^ or ¥ 4 ¥ , ^, § T . These added give the total conduc- 
tances ;= -^ = f . The inverse of f is | = 2|. The total resis- 
tance of the group of three wires is 2| ohms. Ans. 

In a case of two similar wires in parallel the conducting 
power is exactly doubled, while the resistance is reduced to 
one half. 

RULE 11. — The joint conducting power of two wires in 
parallel equals the sum of the individual resistances, divided by 
their product. 

The inverse of this ratio gives the joint resistance. In a 
compound circuit, where some parts are in parallel, their 
resistance must be regarded, in calculation of the whole 
resistance, equal to the resistance of a single conductor which 
might replace them without a change in the total resistance. 

* The inverse or reciprocal of 3/4 is 4 3 ; of 3 it is I, 3 ; of W % it is 2, 3. 



64 MODERN ELECTRICITY 

EXAMPLE 15. 

How shall 6 Daniel cells, of 1-08 volts and 0-6 ohm resist- 
ance each, be connected to drive the greatest current through 
a circuit of 3 ohms resistance ? 

1*08 1*08 * 
The current of one cell = — — — — = -^-7- = 0*3 amp. 

3 + 06 3*6 

Therefore, if we arrange the cells 

6X 1'08 6-48 

a. 6 in series. /= ^ , ,, — ttt-t: = ~v~7 = 0'98 amp. 

3 + (6X0 6) 6-6 K 

b. 2 parallel sets of 3X1-08 _3*24 

3 cells in series, J 3^6 " ^9 " °' 83 amp ' 

3+_ 2~~ 



c. 3 parallel sets of r _ 2X1*08 2* 16 

3 + 



1 series, 7 2X~0-6 ~~ ^4 ~ °' 63 a ™ P ' 



-I z • 11 1 r 1'08 1-08 „ oc . 

rf. 6 in parallel, / = = — — = 35 amp. 

3 + (0 6 h- 6) 3.1 ( a p proxima tely) 

The arrangement 6 in series gives the greatest current 
Ans. 

A more direct way of figuring out similar problems is made 
possible by 

CADIOT AND DUBOST's FORMULA*. 

a. Total number of cells (jri) equals the product of four 
times external resistance (R), times internal resistance of one 
cell (r), times square of the required current (7) 

divided by the square of the E. M. F. of one cell (£). 

AXRXrXl 2 

»- — si 



ELECTRICAL ENGINEERING 65 

b. Number of cells in series (x) equals the product of twice 
the required current (/) times external resistance (/?), 

divided by the E. M. F. of one cell (2r). 

2X/X R 

xz= —e~ 

c. Number of groups in parallel (y) equals the product of 
twice the required current (/) times internal resistance of one 
cell (r), divided by the E. M. F. of one cell (£). 

2X/Xr 

EXAMPLE 16. 

12 electric fire alarm bells, each of nine ohms resistance 
are connected in parallel on a wire of 0*25 ohm resistance. 
What is the least number of 2-volt cells of If ohms resist- 
ance (r) each, required to send a current of 0.25 amp. 
through each bell ? 

Each bell requires 025 amp.; 12X0-25 = 3. Each bell 
has 9 ohms resistance ; x 9 2 = 75 ohms. Therefore : 

#=075 +0-25= 1 ohm; r = If ohm; 
E of each cell = 2 volts ; 7=3 amp. 

According to Cadiot and Dubost's formula b, 

21 R 2X3X1 _ 



x = 



and formula c, _ 2 I r __ 2X3 X 1§ 



2 
r 2X3X I£_ 



E 2 

5 groups in parallel, each of 3 cells in series. Ans. 

EXAMPLE 17. 
8 cells of 2 volts E. M, F. and 2 ohms internal resistance 
each are arranged in two parallel sets, each of 4 cells in 



66 MODERN ELECTRICITY 

series. What current will flow through an external resistance 
of 1 ohm ? 

E of each series 4X2 = 8 volts 

int. resistance 4X2 = 8 ohms 

E of battery 8 volts 

total resistance (8 h- 2) + 1 =4 +1 = 5 ohms. 

r E 8 1 a 



EXAMPLE 18. 

18 electrolytic vats, each of which requires 100 amperes at 
a pressure or 6 volts, are supplied by a dynamo with a current 
of 400 amperes at a pressure of 12 volts. How are the vats 
connected up? 

The conditions are the same as where 18 cells drive a 
motor under the same circumstances. Therefore, 

6 12 3 

r = — — = 0-06 ohm ; R = -— = — — = 0*03 ohm. 
100 400 100 

The total number of the cells (N) multiplied by - , equals 

the square of the number. /« series (n s ). 

r 
The total number of the cells (jV), multiplied by — , equa.'s 

R 

the square of the number of groups in parallel («/). 
. NXR . NXr 



n s ={»M=4 



f V R V 0-03 



18X0-03 


0-06 


18X0-06 



ELECTRICAL ENGINEERING £7 

Multiplying both dividends and divisors by 100, the square 
of 10, which operation does not change the ratio, we get 

6 groups in parallel of 3 vats in series. Ans. 

EXAMPLE 19. 

A battery of 15 cells in series, of 1-8 volts pressure on open 
circuit and 02 ohm internal resistance each, supplies a 
magnet coil of 1-5 ohm resistance, through a wire of 0-5 ohm 
res. What pressure is in the coil ? 

The E. M. F. of the battery, E, = 15 X 1-8 = 27 volts; 

battery resistance, r, = 15 X0*2 = 3 ohms 

external, resistance, R, = 1*5 + 0*5 == 2 ohms 

total resistance = 3 + 2=5 ohms 

coil resistance = 1*5 ohms. Therefore, the coil, 

1*5 1*5 

offering only — - of the resistance, requires only — of the 

E. M. F. 5 5 

1.5 w ^ 40-5 

4-X-27 == —=r = 8- 1 volts. Ans. ■ 
o 5 

Fall of Potential 

58. If it requires 16 pounds pressure to make 400 gallons 
of water per minute flow through a pipe 200 ft. long, 8 pounds 
pressure will make the same quantity of water flow through 
100 feet of the same pipe, 4 pounds for 50 feet, 2 for 25, 1 
for 12£. If pressure gauges were placed at each interval of 
12^- feet, each following gauge would show one pound pressure 
less. The same is true of an electric current. If a wire 20 feet 



68 MODERN ELECTRICITY 

long is connected at one end (A) to the positive pole of a 
battery furnishing a current of 1 volt pressure, the negative 
pole of which is grounded, and the other end (B) to the 
ground, then the pressure at A will be 1 volt and at B it wil. 
be 0. At the middle of the wire (C) it will be £-volt, half-way 
between A and C f-volt, between C an B £-volt. 

RULE 12. — The pressure Jails directly as the resistance 
passed over. 

Units of work and power 

59. The work done by a pump is measured by foot 
pounds. A foot pound is the quantity of work done by a 
force, equivalent to one pound in weight, moving a body through 
a distance of one foot. A gallon of water weighs about 8^- 
pounds ; if therefore 120 gallons (=1000 pounds) of water per 
minute are forced through a pipe by a pressure equivalent to 
33 feet of head, the amount of work done equals 33,000 foot 
pounds per minute. This rate has been adopted as the unit 
in measuring mechanical work, and is called one horse 
power. A horse power hour is 60 times this amount. If a 
pu^.p nfts 600 gallons of water (= 5000 pounds) per minute 
20 feet, the pumps works at a rate of a little more than 3 
horsepower. (20X5000=100,000, while 3 horse power = 
99,000.) (Metric H P = 75 kilogram meters per second.) 

Similarly, when the quantity of electricity conveyed by one 
ampere in one second, or one coulomb, is passed through a 
wire under a pressure of one volt, the quantity of work done is 
called a joule (after the English scientist Joule). The 
amount of power required to do work at this rate, is called volt- 
ampere or watt, after James Watt, the inventor of the con- 




ELECTRICAL ENGINEERING 59 

dsnsing steam engine. One horse power equals 746 watts. 
The kilowatt (= 1000 watts) is a little over 1^- horse power 
(746 + 249 = 995). 

RULE 13. — The power required to keep a steady current 
flowing through a wire, is calculated by multiplying the amperes 
of the current by the volts of pressure. 



P=IXE. / 



EXAMPLE 20. 

a. If a current of 30 amperes is to flow through a circuit 
under a pressure of 90 volts, the power required is = 2700 
watts. P=IXE. 

b. A dynamo which gives out 80 per cent of the power 
supplied by a 30 horse power engine, develops 17,904 watts. 

c. If a dynamo develops 600 kilowatts and the pressure is 

P 
30 volts, a current of 20 amperes will result. /=-£.' 

E 

d. If a current of 8 amperes requires 440 watts, the pres- 

p 
sure will be 55 volts. E = y' 

e. If 3000 coulombs pass through a circuit each second, 
under a pressure of 9 volts, 97,200,000 joules will be 
expended in an hour. [3000 (coulombs) X 9 (volts) X 3600 
(seconds).] 

EXAMPLE 21. 

What current is used by each of 80 incandescent lamps 
requiring 100 volts each, and connected in 40 parallel sets 
of 2 lamps in series, when the power used amounts to 4 
kilowatts ? 



70 MODERN ELECTRICITY 



Pressure. 


Resistance 


For one lamp . E = 100 


R 


For two lamps in 
series, 


2R 


For 40 parallel 
sets of 2 lamps 


2 R 
40 


in series, . . 



Current. 
E 

R 

2jE = £ 
2 R R 

2E 80E 40E 



2R 2R R 

40 

Now, current = watts divided by volts, therefore 

, 4000 _ Jon 40 E 40X100 
= "200 = amperes, and 20 = -^- = - — 

4000 ^ 4000 or ^ . 

20 = — /?= "2Q- = 200 ohms. 

100 ( volts ) nc A 

/ of one lamp = ——-^-r — ^ = 05 ampere. Ans. 

200 (ohms) 

EXAMPLE 22. 
How much silver will be deposited in two hours, when one 
horse-power is applied to an electrolytic vat at a pressure of 
1-86 volts? p ?46 

1 H-P = 746 watts; / = --=-—-= 400 amperes. 

C 1 'OO 

Amount of silver deposited by 1 ampere in 1 hour : 4*026 
gr. (see § 48.) 

2 X 400 X 4-026 = 3220-8 grammes. Ans. 

Electrical energy converted into heat 

6o. In example 20& a dynamo' is supposed to develop 80 
per cent of the power supplied by the engine. The other 20 
per cent cannot be utilized, and is lost, in one sense of the 
word. But no energy is ever destroyed. In this case it is con- 
verted into heat, in overcoming the friction of the dynamo 
bearings, the resistance in the wire, etc. ; a dynamo in opera- 



ELECTRICAL ENGINEERING 71 

tion is always warmer than the surrounding air. A gimlet used 
in boring a hole through wood gets hot, which means that a 
part of the energy applied to it is converted into heat by the 
friction that must be overcome. A nail driven into hard wood 
by hammer blows gets warm, which means that not all the 
power applied is actually used in driving. In the same way, a 
wire becomes heated when electricity passes through it. 

RULE 14. — The amount of heat so produced is proportional 
to the number of watts expended in passing the current through 
the resistance. 

If no work is done by the current, that is to say, if all the 
power is converted into heat, then the amount of heat is equal 
to the number of watts. 

The formula for this law is again derived from Ohm's law : 
E = IXR. Multiplying both sides of this equation by I, we 
have IXE = IXIXR, or E 1=1* R. 

P=IXE (see § 59) ; P= 7 2 R or, in words, 

RULE 15. — The power required to overcome the resistance 
of a wire equals the square of the current in amperes multiplied 
by the resistance in ohms. 

This amount of power, not utilized in the actual work to be 

done, is called the / square R loss 

From Ohm's law another formula for the loss may be 
derived : £ 

/ = — P=I E, and by substituting 

R 

E E 2 

ifor/. P = %- 

R R or, in words, 

RULE 16. — The 1 square R loss equals the pressure squared 
divided by the resistance. 



72 MODERN ELECTRICITY 

EXAMPLE 23. 

If a current of 75 amperes passes through a resistance of 6 
ohms, 33750 watts are expended in heating the wire. 

(P=/a R; 75X75X6=33,750.) 

EXAMPLE 24. 

If power is delivered to a circuit at a pressure of 450 
volts and the resistance of the wire is 5 ohms, the power 
expended amounts to 40*50 kilowatts. (450 X 450 -s- 5.) 

Joule's law 

6i. The amount of heat generated in a wire by the electric 
current can be measured by a calorimeter. This is a device 
consisting of a jar nearly filled with water, in which a centi- 
grade thermometer is immersed, and through which a wire 
runs in loops. The amount of heat needed to raise the tem- 
perature of a gramme of water one degree centigrade (as from 
0° to 1°) is called a calorie. A certain percentage of the 
heat is lost, of course, through radiation. 

RULE 17. — Heat amounting to 0-24 of a calorie equals 
the work represented by one joule, 

(which also means: 1 calorie = 4*2 joules), and the sum of 
calories produced in one second in the calorimeter is, there- 
fore, 0-24 times the power expended : 0*24 I 2 R % This 
value is multiplied by the number of seconds. The formula is 
H='24 7 2 R T (H = heat; T = time.) 

EXAMPLE 25. 

An incandescent lamp of 150 ohms resistance uses 1 

ampere. How much heat does it give off every half-hour? 

H= 24 7 2 R T= -24X 1 X 150X 1800 

= 64,800 calories. Ans. 



ELECTRICAL ENGINEERING 73 

In a circuit having a resistance of 6 ohms, through which a 
current of 20 amperes flows for one-half hour there will be 
developed 1,036,800 calories of heat. (-24X400X6X1800.) 

From the formula H=24 I 2 R T another formula is 
derived : 

/*=//-?- -24 R T 



or, in words, the square of the current in amperes equals the 
calories divided by -24 times the resistance multiplied by 
the time in seconds. 

Heat amounting to -24 of a calorie equals one joule; a 
joule (watt-second) per second equals one watt ; a watt means 
the flowing of one ampere under the pressure of one volt, 
therefore, a watt produces -24 of a calorie every second. 

EXAMPLE 27. 

How much greater is the heating effect of a current of 32 
amperes than that of one of 8 amperes, in a wire of 10 ohm 
resistance ? No time is mentioned. 

32X32X 10 = 10,240 

8 X 8 X 10 = 640 

10,240-*- 640 = 16 times as great. Ans. 

EXAMPLE 28. 

What part of the total power supplied to 50 incandescent 
lamps, connected in parallel, with a resistance of 180 ohms 
each, is lost in a wire having a resistance of 0.6 ohm ? 

ISO 360 , 
Lamp resistance = — — - = -— = 3-6 
F 50 100 

Wire resistance = 0*6 

Total resistance = 3*6 + 0-6 = 4.2 

0-6 is one-seventh of 4-2. \ or 14-28 per cent. Ans. 



74 MODERN ELECTRICITY 

EXAMPLE 29. 

How much heat per minute is generated in an electrical 
heating apparatus using 6 H. P. ? 

1 H. P. = 746 joules per second. 

6 H. P. = 6 X 746 = 4476 j. p. s. 

60 X 4,476 = 268,560 joules per minute. 

0.24 X 268,560 = 64,454 cal. Ans. 

EXAMPLE 30. 

A battery raises the temperature of 1 ,000 grammes of 
water in a calorimeter 6° C. in ten minutes. If one-seventh 
of the total heat generated is lost by radiation, how much 
power is supplied to the coil by the battery ? 

Raising the temperature of one gramme of water 1° C. in 
one second requires 4*2 joules. Therefore, to raise the 
temperature 

of 1 ,000 gr. 1 ° C. in 1 second, requires 1 ,000 X 42 joules 

" 1,000 gr. 6° C. " 1 " "6X1,000X4-2 " 

" 1,000 gr. 6° C. " 10 minutes » 6 X 1 ,000 X 4-2 •• 

600 

'—— = 10 X 4*2 = 42 joules per second. 

600 

One seventh being lost, 42 = $ ; total heat = 49. 

49 joules per second- = 49 watts. Ans. 

62. A wire through which a current flows, gives out a part 
of the heat developed in it. When it gives out as much as 
is developed, it remains at a fixed temperature. An insulated 
wire gives out more heat than one not insulated, because the 
insulation being quite thick as compared with the wire itself, 
offers a much larger surface than the wire, and the increased 
radiation more than balances the increased difficulty of the 
heat in reaching the surface. 



ELECTRICAL ENGINEERING 75 

Thermoelectric current 

63. When a rod of bismuth is soldered, end to end, to a rod 
of antimony, and the two free ends are connected by a wire, 
and the junction is heated, a current flows through the whole 
circuit in the direction from bismuth to antimony. If the junc- 
tion is cooled, the current flows from antimony to bismuth. 
On the other hand, if a current is sent through such a rod in 
the direction from bismuth to antimony, the junction becomes 
cooled; when from antimony to bismuth, the junction is heated. 
This is true of all combinations of metals which are thermo- 
electrically affected. It is also true, in a minor degree, of 
two different kinds of the same metal, of two liquids, and of 
a liquid and a metal. 

In the following contact series of metals in air each metal 
named is electro-positive in regard to all that follow it and 
electro -negative to all that precede it: Bismuth, zinc, lead, 
copper, iron, silver, platinum, antimony. Bismuth and anti- 
mony, being farthest apart in the series, give the best results. 

RULE 1 8. — The difference of potentiai, produced by the 
contact of any two metals, is equal to the sum of the differences 
of potentials between the intervening metals in the constant 
series. (Volta's law.) 

Here follows a table of the differences of potential set up 
by contact of some of the metals : 

Zinc » Iron f , 46 

Lead ) Copper ) 



[-069 ST" J- 238 

) Platinum ) 



b" ST}-"* 



76 



MODERN ELECTRICITY 




Fig. 19. 



According to Volta's law, the difference in potential 
between zinc and tin is .210+ -069 = 279 ; between zinc and 
iron, -210 + -069 + -313 = -592, etc. 

Such a pair is called a thermo-electric couple. The 
power of any thermo-electric couple, as a rule, increases with 
the increase of difference of temperature between the junction 
and the other ends, up to certain limits, beyond which the cur- 
rent may cease altogether, or flow in the opposite direction. 

A circuit of several such couples is 
called a thermopile. (See diagram, fig. 
19.) They are so arranged that one set 
of junctions (the first, third, fifth, etc.) 
can be heated, while the other set (the 
second, fourth, sixth, etc.) are kept cool. 
The E.M.F. generated by a couple is so low that it is measured 
in microvolts (millionths of a volt), but they are very con- 
venient in laboratory work, especially for discovering minute 
differences in radial heat, because the current set up may 
be kept perfectly constant, as by putting the even numbered 
junctions in boiling water and the odd numbered ones in melt- 
ing ice. Some thermopiles are so sensitive that they will 
indicate a difference of temperature of -5-0V0" °f a degree. 

Questions and Answers. 

Q. What is the resistance in one mile of No. 1 B & S 
(Amer. standard wire gauge) trolley wire ? (See page 208.) 

A. Between 6 and 7 tenths of an ohm 

Q. If a current of 6 amperes flows through a wire of 10 
ohms resistance, what will be the pressure ? A. 60 volts. 

Q. In a battery of 4 gravity cells in series each cell 
has an internal resistance of 4 ohms, and gives 1-5 volts 



ELECTRICAL ENGINEERING 77 

pressure. The external resistance is 8 ohms. What current 
will flow ? 

A. \ ampere. 

Q. If a battery of 4 cells in series, of 1-5 volts each, 
develops a current of 6 amperes, what is the resistance in each 
cell, the external resistance being negligible, that is, too small 
for consideration ? 

A. \ ohm. 

Q. What does E = I X R mean ? 

A. It means that the electrical pressure in volts between 2 
points in a circuit can be calculated by multiplying the current 
flowing in that part, in amperes, with the resistance, in ohms. 

Q. Through a copper wire 2000 feet long, with a cross sec- 
tion of 25,000 circular mils, flows a current of 60 amperes. 
How great is the pressure? 

A. 50-4 volts. (R= 10 * 5 >< J^ = |~ = ' 84ohms ; E=z 

0-84 X 60 = 50-4.), 

Q. A wire has a resistance of 150 ohms. A piece of the 
wire 10 feet long has a resistance of 2 ohms. How long is 
the wire ? 

A. 750 feet. (150-^2 = 75; 75 X 10 = 750.) 
Q. A dynamo of 9 ohms resistance supplies 12 eight- 
ampere arc lamps, each requiring 50 volts and connected in 
series. The copper wire has a cross section of 12,000 c. m. 
and is 6,000 feet long. What is the total pressure? 

A. 714 volts. (The resistance of the wire = 10-5X — = 

1 z. 

12 X 50 

5*25 ; that of the lamps = = 75 ; that of dynamo 

8 

= 9. Total 89-25 ohms. £ = 8 X 89-25 = 714.) 



78 MODERN ELECTRICITY 

Q. A single incandescent lamp is supplied with a current 
of 2 amperes. The copper wire circuit is 2000 feet long, 
cross section 5000 c. m. The pressure is 200 volts. What 
is the hot resistance of the filament ? 

A. 95-8 ohms. (Total resistance = 200 -*- 2 = 100; wire 

2000 
resistance = 10-5 X— — = 4-2 ; 100 — 4-2 = 95-8.) 

ouuu 

Q. What is the joint resistance of 4 parts of a circuit in 

series, when their respective resistances are 5, 4, 2 and 1 

ohms? And what is it when they are connected in parallel, 

with 10-volts pressure at their terminals? 

A. In series, 12 ohms (5 + 4 + 2+1). In parallel, 0-5 

10 10 10 
ohm. (The currents in the parts are — — f- — _|_— + 10 ~ 

O T 1 z* 

19'5 amperes; — — = 0*5. Or: The conductances of the 

1 1 1 39 20 

parts are r+7 + o+l = ^7v The reverse of this is — = 0*5.) 

1 8 

Q. What is the inverse of -, 29, - ? 

o o 

A3 13 
A - J '29' 8' 

Q. What is the joint conductance of 2 branches receiving 

12 volts, and with 6 and 18 ohms resistance respectively? 

And what is the joint current and joint resistance ? 

4 
A. Joint conductance-—; joint current 2§- amperes ; joint 

18 



6 "~18~ = 18 ; 6 " " 18 = " 3 

8 3 36 



resistance 4-5 ohms. ~t^— t^I "~7" + ~ = ^ = 2f ; 



12 ^3 = 12X 8=ir =4 - 5 -> 



ELECTRICAL ENGINEERING 79 

Q. The joint resistance of 2 wires in parallel is 3 ohms. 
The resistance of one branch is 5 ohms, what is that of the 
other ? 

i 

A. 7*5 ohms. (Joint conductance -; conductance of 5 

115 13 1#jM 2 . ,. 

ohm wire -; - = — ; e = T^> the difference -— indicates 
5 3 15 5 15 15 

the conductance of the other branch, and the inverse, -~- = 

7*5, is its resistance.) 

Q. Three incandescent lamps placed in parallel, have the 

following resistances : 150, 200, 300 ohms. The voltage at the 

terminals is 120 volts. What is the total current ? 

f 4 3 2 9 1 

A. 1-8 amperes. | -+-+-=-= If = 1-8. | 
[5555 

Q. If the current in a circuit is to be increased one half, 
by placing a similar wire in parallel, without causing a change in 
the drop of pressure, of what size should the second wire be? 

A. One half the cross section of the other, in circular mils. 

Q. Can water be frozen by electricity ? 

A. Yes, by cooling the junctions of a thermopile, as by 
sending a current from the bismuth rod to the antimony rod, a 
drop of water at the cooled junction may be frozen. 

Q. How much voltage does one thermo-electric couple of 
German silver and an alloy of zinc and antimony generate ? 

A. About four-hundredths of one volt. 

Q. What is Mho ? 

A, The unit of conductance, little used because resistance 
impliedly expresses conductance, being its reciprocal. "Ohm" 
spelled backward is "Mho". 



CHAPTER V 3 — Magnetism, 



Theory of magnetism 

64. What magnetism really is, has not been discovered. 
The latest theory, well supported by facts, assumes that the 
molecules of a magnetic substance are minute magnets by 
nature, each having two poles. In a bar magnet each mole- 
cule at the two ends may 
be supposed to have the 
attraction of its inward- 
pointing pole neutralized 
more strongly than that of 
the outward-pointing pole, 
which, therefore, is free 
to attract other bodies. 
A certain native oxide of 
iron is called magnetite, 
because pieces of it (lode- 
stones or leading stones) 
sometimes are natural 
magnets. Such a natu- 
ral magnet changes a 
FlG - 20 - magnetic piece of soft 

steel or iron to an artificial magnet, without losing any part 
of its own magnetism. The steel magnet is a permanent 
magnet, the one of soft iron loses almost all its magnetism, 
as soon as the contact with the natural magnet ceases. The 
ancients found this stone near Magnesia in Asia Minor, hence 

80 




ELECTRICAL ENGINEERING g^ 

the name. It is occasionally found in Sweden, Spain, Arkansas 
and the Isle of Elba. 

A horseshoe magnet (see fig. 20) is a steel bar magnet, 
the two ends of which are bent close together. The advantage 
of a horseshoe magnet lies in the fact that a piece of soft iron 
placed across its poles is a strong protection of its magnetism. 
The piece of soft iron is called a keeper or armature. 

Terrestrial magnetism 

65. A magnetic bar ( needle ) properly suspended on a 
thread, will turn so as to point almost exactly north and south, 
and in the northern hemisphere the north-seeking pole of the 
magnetic needle dips down (inclination), and the more the 
closer it is to the geographical North Pole. On the southern 
hemisphere the sow//z-seeking pole dips. All this proves that the 
earth is a magnet of two poles. But its geographical and 
magnetic poles are not identical ; nor are the magnetic poles 
constant : they vary back and forth in the course of time, 
and in different longitudes (declination). 

Magnetic induction 

66. If two magnetic needles properly suspended are placed 
near each other, the two north poles or south poles repel 
each other, while the north pole of one needle will attract 
the south pole of the other. Judging from this, the north- 
seeking pole of a magnetic needle has not the same mag- 
netism as the north pole of the earth. 

RULE 18 A. —Like poles repel, unlike poles attract each other. 

(Compare Rule 1 in § 5.) If a soft iron bar is substituted 
for one of the magnetic needles, the result is quite different : 

Either end of the bar will attract either pole of the needle. 



82 MODERN ELECTRICITY 

The magnetic needle magnetizes the bar by induction ; and 
if a steel magnet is substituted for the needle, the induction 
will be strong enough to cause the soft iron bar to magnetize 
another soft iron bar to a lesser degree, and this one will 
magnetize a third bar by induction to a still smaller degree, 
and so on. This decrease in strength is due to the fact that 
in each bar the attracted end is nearer to the inducing link 
in the chain of bars than the repelled end, and the attraction 
is therefore stronger than the repulsion. 

Each magnetized body has two opposite poles. If a steel 
magnet is broken in two, each piece is at once a magnet with 
two poles. If a soft iron bar is touched at its two ends by 
two steel magnet north poles of equal strength, the two 
ends of the bar become south poles, and in the middle of 
the bar a north pole is formed; it is called a consequent pole. 

Magnetic substance 

67. Substances capable of becoming magnetized by induc- 
tion are called magnetic material. Of all these, iron in ail 
its forms stands at the head. Nickel, cobalt, platinum and a 
few other substances are magnetic in a far lesser degree. 
Magnetism acts through paper, wood, a vacuum, and, in short, 
through all materials that may not be magnetized. As seen 
in §64, magnetic materials differ in their power of retaining 
magnetism ; they differ also in their power of resisting mag- 
netization. Hard steel is difficult to magnetize, but it also 
retains magnetism very strongly ; it is said to have great 
coercive force ; soft iron is easily magnetized and demag- 
netized. (See 72.) Sudden shocks, as by dropping on a 
hard ground, or great heat will deprive a magnet of its force. 
A steel bar may be magnetized by stroking one end from the 



ELECTRICAL ENGINEERING 83 

center with one pole of a magnet, and the other end from the 
center with the other pole, or by laying it against an electro- 
magnet, or by placing it within a coil of wire carrying an 
electric current. A very strong magnet can be made by 
placing several thin magnetized bars of even length one upon 
the other. The reason for this is that the magnetic force 
appears on the surface of each bar. Such a magnet is called 
a compound or laminated magnet. When a steel bar has 
been magnetized to its full capacity, it is said to be saturated. 
It will lose part of this strength again, until it reaches its 
proper strength, which is then permanent. When it has 
reached its permanent strength it is said to be aged. Steel 
magnets are aged artificially by immersion in steam for a 
length of time. 

Magnetic field 

68. In keeping with the theory set forth in § 64, the mag- 
netic force in a steel bar magnet shows most strongly at its 
ends, but it extends in ever decreasing degree towards the 

^ft^^lft magnet' " ~W l 




Fig. 21. 

middle. If iron filings are strewn on a paper placed on a mag- 
net, this fact becomes at once evident from the quantity of 
filings gathering at different points. (See fig. 21.) It is also 



84 MODERN ELECTRICITY 

evident that the filings place themselves in a certain order rep- 
resented by curves reaching from one pole to the other. These 
lines are called lines of (magnetic) force, and the space in 
which a magnet may create such lines, is called a magnetic 
field of force. The strength of this force decreases with 
the increasing distance from the pole. Abnormally a mag- 
netic bar may have one or more intermediate points of maxi- 
mum attraction, which are then called consequent (=one 
following upon another) poles. See § 66. 

Any small, thin, needle-like piece of iron thrown on the 
paper will place itself in a position tangential to the curve 
nearest which it was dropped. If a free-swinging magnet is 
brought within the field of force of another magnet, it will 
set itself so that its own lines of force are parallel to those 
of the other, and in the same direction. A few light iron 
filings floating on a water surface organize at once into 
a compact body when a magnet is held near them, and 
assume a north and south position, when the magnet is 
removed. If the magnet is moved about, some of the filings 
swing completely around. 

Measures of magnetism 

69. In order to arrive at a standard of measure for mag- 
netism, the magnetic field is imagined to be filled with so 
many lines of force per square centimeter, and a unit field 
is imagined to have one line of force per square centimeter. 
A magnet pole is said to have unit strength, when it repels 
or attracts another similar pole, placed at the distance of 
one centimeter in air, with a force of one dyne. (A dyne is 
the force which, acting on a body weighing one gramme in 
one second, imparts to it a velocity of one centimeter per 



ELECTRICAL ENGINEERING 85 

second.) Of course, two such poles cannot be constructed 
in practice, as magnets of only one pole cannot be made. 
The number of lines of force in a square centimeter of 
cress section of the field determine the magnetic density ; 
if it is uniform, the field is called uniform. The total uumber 
of lines in the whole field are called the magnetic flux, or 
simply the magnetism. As seen in § 68, the lines of force 
reach from one pole to the other, and, as in electricity, 
see § 14, the magnetic pressure is due to a difference of 
potential. This pressure is measured by the work necessary 
to move an independent north pole of a certain strength from 
the south to the north pole of the magnet. This amount of 
pressure is called a magnetic unit. 

Electromagnetism /V , 

7o. A close relation appears to /^^r 

exist between magnetism and / \krl ^ 

electricity. In the scientific world \3^ ~ I~ 

this was first established in 1819, ( ^z2^p===~y 

when a Danish investigator, Oer- JL* 

sted, announced that a compass 22 

needle is disturbed by the neigh- 
borhood of an electric current. If the wire through which 
the current flows is held above and parallel to the needle 
the needle tends to set itself at right angles to the wire, 
(See fig. 22.) The degree to which it does this, depends on 
the strength of the current in the wire and on its nearness. 
If the current is just strong enough and near enough to 
balance the magnetism of the earth, the needle will deflect 
45 degrees. The explanation given for this phenomenon is 
that the current creates another magnetic field ( see § 68 ) 



86 



MODERN ELECTRICITY 



3» > 

N 




w\ •• 




-^-^Sr 


s 



Fig. 23. 



the force of which affects the needle. The reason for this 
fact, science has not fathomed. The lines of this electro- 
magnetic force in the field about a round 
wire must necessarily be concentric cir- 
cles around the wire, as the direction of 
the force on all sides is at right angles 
to the direction of the current. If the 
wire of a battery is passed vertically 
through a piece of cardboard placed hori- 
zontally, (see fig. 23.) on which iron 
filings have been strewn, the filings will 
arrange themselves in concentric circles 
as soon as the current is turned on. 

All that is stated in §68, applies here. If we place a 
compass needle on the card board, with its pivot directly 
over a curve of filings, as shown in the figure, it will tend 
to place itself in a position tangential to the curve. The north 
pole of the needle in the figure points West ; if placed East 
of the wire, it would point South. If, however, the current 
were flowing in the opposite direction to that indicated by 
the arrows, the needle would point East in the position 
shown, and if placed East of the wire, would point North. 
Ampere's rule for determining the direction in which the 
needle will deflect : 

RULE 19. — Suppose yourself to be in the wire, floating 
with the current and facing the needle ; its north pole will 
turn toward your left hand. 

The fact may also be remembered as foljows : Grasping the 
wire with the right hand, so that the thumb points in the 
direction in which the current flows, and the fingers enclose 



ELECTRICAL ENGINEERING 87 

the wire, the finger tips point in the direction in which the 
North pole of the needle will deflect. Based on the first rule 
is the common method of determining the direction of a cur- 
rent in a wire by placing a compass under the wire. 

If two thin wires are loosely suspended near each other, 
and a current is sent through them so as to flow up in one 
and down in the other, the two will repel each other ; if 
the current flows in the same direction in both, they will 
attract each other. Wires inclined to each other tend to 
become parallel. A flexible charged wire will wind around 
a fixed magnet. All the facts mentioned in this section, 
are of the greatest importance, for from them is derived 

RULE 20. — Magnetic lines of force tend to occupy a posi- 
tion in which they are parallel with each other and run in the 
same direction. 

Apparently the lines of force cannot become parallel or 
point in the same direction, when the two conductors are at 
an angle, or too close together, or too far apart. 

The Solenoid 

71. If a charged wire is placed above a magnet, and 
another below it, at the same distance, their influence on the 
magnet will be twofold, according to Ampere's rule : If the 
currents flow in opposite directions, the influence will be 
doubled ; if they flow in the same direction, the two influences 
will balance or neutralize each other, and the needle will not 
deflect. 

RULE 21. — If one wire is coiled into several Urns 
around the needle, this influence of the current is determined 
by the strength of the current times the number of the turns. 



88 



MODERN ELECTRICITY 



This product is called current turns or ampere turns, 
and the set of coils is called a solenoid. The law stated 
at the end of § 70 applies also in the case of a solenoid : 
within the coils the lines run parallel and in the general 
direction of the current from one end of the coil to the 
other; between the single turns, and outside, the lines of force 

adjust themselves to 
each other. The lines 
of force emerge from 
one end of the sole- 
noid (helix or coil), 
pass around its outside 
and enter the other 
circuit. (See fig. 24.) 
Greek) means " pipe- 




Fig 24. 



end, thus completing the magnetic 
The word " solenoid " (from the 
shaped." 

RULE 22. — The number of lines of force {called induction, 
per square centimeter) set up in an empty helix, equals the 
product of the number of turns ( per centimeter in length of the 
coil) times the number of amperes multiplied by 1.257, When 
the inch is used the constant is 32. 

EXAMPLE 31. 

a. How many turns to the inch are required to set up 
an induction of 400 lines with a current of 5 amperes ? 

One ampere turn gives 32 lines of force ; 400-^3-2 = 125 
ampere turns ; 125-^-5 =25. Ans. 

b. A current of 5 amperes flows through a 24-inch helix of 
192 turns. How many lines of force per square inch inside 
the coil ? 

192 -*- 24 = 8 turns per inch. 8 X 5 X 3*2 = 128. Ans. 



ELECTRICAL ENGINEERING 89 

c. How many amperes will produce 1.000 lines per square 
inch in a coil 15 inches long with 3000 turns? 

1000-^-3-2 = 312-5 ampere turns per inch in length of 
the coil. There are 200 turns per inch (3000 -^- 15). 312*5 
-5-200=1-56. Ans. 

k 

A solenoid is in every respect exactly like a steel mag- 
net, and all that has been said about the latter, applies to 
the solenoid as well. The direction in which the current 
flows through it, indicates the polarity: 

RULE 23. — - For a person standing at the south pole, the 
current flows in the direction in which the hands of a clock 
turn, from the left over to the right. 

The Electromagnet 

72. When a bar of iron or steel is placed within a sole- 
noid, the electric current magnetizes it strongly ; the lines of 
force produced are enormously increased in number. This 
power of iron is called its permeability. Bodies in which 
the magnetizing force produces a large quantity of lines of 
force, are said to possess a high permeability. The more 
ampere turns, the more readily will the bar be saturated. 

It was stated in § 69 that magnetism is due to a difference 
of magnetic potential. Therefore we may safely assume 
that a solenoid produces such a difference, and experiments 
have proved that 

RULE 24. — one ampere turn sets up almost exactly one 
and one-quarter units of magnetic pressure. 

The formula used to express this law is Af= 1*256 n i, 
M representing the magnetic pressure, n the number of turns, 
/the current in amperes, and n /', therefore, the ampere turns. 



90 MODERN ELECTRICITY 

From the above it will be readily uderstood, that a bar 
of soft iron wound with a large number of turns, through 
which a strong current flows, will become a magnet of enor- 
mous strength. Of equal importance is the fact (discovered 
by the English scientist Sturgeon, 1825) that while a steel 
bar retains its magnetism after the current is shut off, a 
soft iron bar instantly loses almost all its magnetism. On 
these two facts, furnishing a perfectly controllable force, is 
based the bulk of the magnificent modern electric achieve- 
ments. The insignificant amount of magnetism retained by 
the soft iron bar, when the current is shut off, corresponds to 
the powerful magnetism retained in a hard steel bar ; they 
are both called residual magnetism. 

Permeability 

73. RULE 25. — The permeability of a bar of iron is 
figured by dividing its number of lines of force by the number 
which pass through the same space when the iron is not present. 

In the case of example 316 in §71, with 45,000 lines of 
force per inch passing, the permeability would be 351. 
(45,000- 128 = 351.) 

There is no substance, that comes near iron in magnetic 

permeability. Nickel and cobalt, next in order, have a much 

lower permeability. Wrought iron has the greatest, then 

steel, then cast iron. The purer the iron the greater is its 

permeability, or the smaller its reluctance, which term 

means the same in magnetism, as resistance in electricity. 

The reluctance of a material is the inverse of its permeability; 

therefore, the . .",._, 

1 length in inches (or cm. 

reluctance = — — X 



permeability cross section in sq in. (sq cm ) 



ELECTRICAL ENGINEERING 



91 



Up to the point of saturation of the electromagnet with 
magnetism, there is naturally a great variety of permeability 
(the amount of magnetism produced by currents of various 
strength ): in a non-magnetized bar a slight current will create 
a large quantity of magnetism ; the more magnetized the 
bar becomes, the smaller the effect of the increasing strength 
of the current ; after saturation even a current of greatly 
increased strength will cause only a slight rise of the mag- 
netic pressure. 

The saturation curve 

74. For each kind of iron its permeability may be indirectly 
established by drawing a curve corresponding with its relations 
between ampere turns and 
magnetism. In fig. 25 dis- 
tances on the lines across the 
page (horizontal) indicate the 
ampere turns per inch of the 
length of the helix, and dis- 
tances on the vertical lines 
indicate the number of lines 
of force per sq. inch or cm. 
in the iron. The curve C B, 
therefore, indicates the average 
induction per square inch of soft iron which will be produced 
by a certain number of ampere turns per inch of its length. 
Near point A will be the point of saturation, with 12,000 
lines per sq. c. m, indicated at six ampere turns per sq. 
centimeter. A curve similar to C B may be constructed 
from experiments, indicative of the rate at which the 
magnetism leaves the iron, when the current is gradually 



15000 



12000 



9000 



6000 



3000 



ill 



2 4 6 8 10 12 14- 16 18 
MAGNETIZING FORCE 
Fig. 25. 



92 MODERN ELECTRICITY 

diminished and finally shut off entirely. The deviation of 
this curve from the path of curve C B is called hysteresis, 
and is due to the coercive force of iron. (See §67.) 

By dividing the indicated number of lines of force per 
square centim. by the indicated magnetizing force per square 
centim., we arrive indirectly at the permeability of a piece 
of iron at any point of the saturation curve. — The mag- 
netizing force per square cm. is found by multiplying the 
ampere turns per cm. in length by 1.257 

75. Air, as compared with iron, has a very low permea- 
bility, and has therefore been taken as unity (1). Materials 
that have a greater permeability than air are called para- 
magnetic, those having a less permeability are called dia- 
magnetic. But all substances, even a vacuum, have some 
degree of permeability, so that there is no insulation possible 
in magnetism, as there is in electricity. 

RULE 26. — The permeability of any piece of material 
increases with the increase of cross section and decreases with 
the increase of length. 

76. Saturation curves have been fixed for all the impor- 
tant kinds of iron, and they are very useful in dynamo cal- 
culations. See §74. The vertical scale gives the number 
of lines per sq cm. or sq inch ; from where a horizontal line 
drawn from there intersects the curve, a vertical line drawn 
downward to the horizontal scale marks the number of 
ampere-turns required per cm. or inch in length of the 
magnetic circuit in the ring. 

The number of ampere-turns needed to drive a given 
number of lines of force through an iron ring, is calculated as 



ELECTRICAL ENGINEERING 



93 



follows : Divide the number of lines by the number of square 
inches cross section of the ring. This gives the induction 
per square inch. Then find on the saturation curve of the 
iron the number of ampere turns per inch, in length cor- 
responding to this induction per square inch, and multiply it 
by the medium length of the magnetic circuit in the iron 
ring in inches (the length of a ring of d inches in diameter 
equals it X d or 3-1416 times diameter). The result is the 
answer required. 

RULE 27. — To find the permeability of a bar of iron at 
any point of the saturation curve : 

a, if the curve is given in terms of lines per sq. cm., and 
ampere turns per cm. in length, divide the number of lines of 
force per sq. cm. by magnetizing force per sq. cm. 

b, if the curve is given in terms of lines per sq. inch and 
ampere-turns per inch in length, divide the induction per sq. inch 
by the magnetizing force per sq. inch, which equals the ampere- 
turns per inch in length times 3-2. 

RULE 28. — a. To reduce from lines of force per sq. cm. 
to lines of force per sq. inch, multiply by 6-45. 

b. To reduce from lines of force per sq, inch to lines of 
force per sq. cm. divide by 6-45. 

c. To reduce from magnetizing force per sq. cm. to ampere 
turns per inch in length, divide by 3-2 and multiply by 6-45. 

d. To reduce from ampere turns per inch in length to magnet- 
izing force per sq. cm., multiply by 3-2 and divide by 6-45. 

Magnetomotive Force 

77. Ohm's law is but an application of the general law 
that the result of any effort is equal to that effort divided 



94 MODERN ELECTRICITY 

by the opposing force, and this general law holds good in 
regard to the electromagnet : 

RULE 29. — The number of lines of force in any magnetic 
circuit equals the magnetic pressure divided by the reluctance. 

M 
(Formula: N= — ; —N representing the number of lines 

of force, M the magnetomotive force or magnetic pressure, 
Fthe reluctance.) The formula for Mhas been stated in §72. 

Of course, from the above formula we also derive : M= 

M 
NXP\ and P = jj- 

EXAMPLE 32. 

a. What is the permeability of iron at 75,000 lines per sq. 
inch, when the ampere-turns per inch in length are 18 ? 

18X3-2 = 57-6; 75 f 000-s-57-6=l,302. Ans. 

b. What is the permeability of cast steel at an induction of 
75,000, with 24 ampere turns per inch in length? 

24 X 3-2 = 76-8 ; 75,000 -s- 76*8 =976 +. Ans. 

c. What is the permeability of cast iron at an induction of 
38,000 lines, with 80 ampere-turns per inch in length. 

80X3-2=256; 38,000^-256=148. Ans. 

EXAMPLE 33. 

How many units of magnetic pressure are set up in a 
copper wire coil of an electromagnet, when the wire has 1200 
turns 2 feet long each and 1 100 circul. mils cross section, by 
a current of 50 volts pressure ? According to § 56, 

2X 10-5 21 
resistance of 1 turn = — = = 0019 ohm. 

res. of 1,200 turns = 1200 X 0-019 = 22-8 ohms. 



ELECTRICAL ENGINEERING 

According to § 72, Mmf = 1-257 n c 

C = J£L therefore Mmf = 1.257 XI 200 X J 



95 



22.8 ' 22.8 

_ 1-257X60000 _ 75420 

22-8 ~" 22-8 

= 3307 units of Mmf. Ans. 

EXAMPLE 34. 

6 Daniel cells, arranged in 3 sets in parallel of 2 cells in 
series, and of a pressure of 1-1 volts, and an internal resist- 
ance of 3 ohms each, are connected to a solenoid of 1000 
turns and 4 ohms resistance. What is the magnetic pressure 
set up? 

E of one set of 2 cells = 2 X 1' 1 = 2*2 volts 
r " "2 " =2X3 = 6 ohms 

E of three sets = 2-2 volts 

r " * = -= 2 ohms 

R = 4 ohms ; total res. = 4 + 2 = 6 ohms 

2.2 

Cof three sets =~~ = 0*366 amperes 
6 

Mmf = 1 -257 X 0-366 X 1 000 

= 1 -257 X 366 = 460 units of Mmf. Ans. 

EXAMPLE 35. 
What is the magnetic pressure set up, if the 6 cells in the 
preceding example are arranged in series ? 

£ = 6X1;I =6-6 volts 

r =6X3= 18 ohms 

R— 4 ohms 

total res. = 18 + 4 = 22 ohms 

E 6.6 
Current C = — — = — - = 0-3 ampere 
K ~r i\ 22 

Mmf= 1-257X0-3X 1000 

= 1 -257 X 300 =377-1 units of Mmf. Ans. 



96 MODERN ELECTRICITY 

EXAMPLE 36. 
A ring of iron 200 cm. long, with a cross section of 30 
sq. cm., and a permeability of 700 when 50.000 lines of 
force pass through it, has wound upon it a coil of 400 turns. 
How much current is required to set up this magnetization? 
Number of lines (§77) = magn. pressure -s- reluctance. 

,o^ 1 v/200 200 2 

Reluctance ( § 73") = ■ X - — = = — - 

^ } 700 30 21000 210 

2 



Number of lines: 50,000 = 1-257 X 400 XC 



210 

_ 210X 1-257X400XC 
2 

= 105X 1.257 X400XC 
= 42000 X 1 -257 X C 
= 52794 X C 
C = 50,000 ^-52,794 
C = 0*95 ampere. Ans. 

If a magnetic circuit consists partly of iron and partly of air 
gaps, as in dynamos, the ampere-turns must be figured for 
each part separately, and the results added up, to arrive at the 
number of ampere turns required to drive a desired number 
of lines through the circuit. The number of lines of force 
per sq. inch in a gap must be multiplied by -3133 (the recipro- 
cal of 3-2) and by the magnetic length of the gap in inches 
or cm. 

EXAMPLE 37. 
A magnetic circuit, partly made up of a U-shaped bar of 
annealed iron 150 cm. long by 20 sq. cm. cross section, 
has a permeability of 3000 at a magnetic induction of 5,000 
lines of force per sq. cm. The remaining parts are two air 
spaces 1 cm. long each. What magnetic pressure will set up 
a total of 600,000 lines oi force ? 



ELECTRICAL ENGINEERING 97 

D 1 f f I l V 150 I50 ] 

Reluctance of iron = -^r-— X -^r = t^^t: — ttzx 

3000 20 60,000 400 

The air spaces must be considered to have the same cross 
section as the iron, of course. 

d i * t • 2>: ! 2 40 

Reluctance of air - 



20 20 400 

total reluctance = — — + — — = — — 
400 400 400 

■600.000X41 ', - 

Magnetic pressure = — = 61 ,500 

400 

61500 units of Mmf. Ans. 

Questions and Answers. 

Q. What is the origin cf the word "magnet"? 

A. It is derived from the Greek word magnes, the name 
of a mineral possessing magnetic quality. 

Q. What is a good way of making a magnet out of a 
steel bar? 

A. Place the bar within a coil of wire through which an 
electric current is flowing. 

Q. How much strength does a well made magnet develop? 

A. It will carry up to twenty times its own weight. 

Q. What would such strength signify? 

A. That the magnet has twenty times the strength of the 
force of gravity due tu the earth. 

Q. What effect has heat upon a magnet ? 

A. Cooling slightly increases the power of a steel magnet. 
Red heat will demagnetize a magnet. 

Q. What is coercive force ? 

A. The resistance of a material to a change in its mag- 
netic strength. 



98 MODERN ELECTRICITY 

Q. Are other materials than metals magnetic? 

A. Yes, oxygen for instance, and some salts of metals, 
also their solutions. 

Q. How many lines of force per sq. cm. are there in a 
field of unit strength ? 

A. It is theoretically conceived to have one line of force 
per sq. cm, 

Q. A field has 50 lines of force per sq. cm., and acts 
upon a pole with a force of 25 dynes. How strong is the pole ? 

A. £ unit. 

Q. If a pole of 2 units strength is placed in a field of 6 
units strength, what force will act upon it? A. 12 dynes. 

Q. Why does not the compass needle point due north and 
south ? 

A. Because the magnetic poles of the earth do not coin- 
cide with the geographical poles. 

Q. Why does not the compass needle show the same 
deflection from a true north and south position on all points 
of the globe ? 

A. Because the lines cf longitude of two places do not form 
the same angle with the straight lines connecting them with 
the magnetic pole. 

Q. Determine the direction of the lines of force by the 
right-handed screw ? 

A. If the current flows in the direction in which the 
screw is turned when driven into the wood, then the posi- 
tive direction of the lines of force is the same in which the 
screw turns. 

Q. If a flexible wire through which a current flows has 
wound around a fixed magnet, what will happen if the direc- 
tion of the current is changed ? 



ELECTRICAL ENGINEERING 99 

A. The wire will unwind and then wind around the magnet 
in the opposite direction. 

Q. What is Ampere's theory of magnetism? 

A. He assumed that the molecules of all magnetic sub- 
stances are at all times surrounded by little electric currents, 
which make them into magnets. Ordinarily these currents 
flow in many different directions, neutralizing each other, but 
when the body is magnetized, the molecules array them- 
selves parallel to each other ana combine their magnetic 
forces. 

Q. On what did Ampere base this theory ? 

A. On the effect which a sol' 6 'oid has upon a bar of soft 
iron placed within it. 

Q. Does this theory explain why the molecules are sur- 
rounded by electric currents, and how these currents produce 
magnetism ? 

A. It does not attempt to answer either question. 

Q. Does the saturation curve give the permeability of a 
piece of iron directly ? 

A. No, indirectly. 

Q. What is the reluctance in a piece of iron 36 inches 
long and 3 sq. inches cross section, at a permeability of 
1000 units? 

A. 1-h 1000 X (36-5-3)= 12 -h 1000 = 0.012 

Q. What kind of an electromagnet will do the best work ? 

A. One, the circuit of which is made up of material of the 
highest permeability, and which is provided with as many 
ampere turns as possible. 



CHAPTER VI. — Electromagnetic Induction 

Invention of Motor and Dynamo 

78. The discovery of Oersted (see § 70) was soon followed 
by the brilliant achievements of Faraday and Henry * in 
making the close mutual relations between magnetism and 
electricity serviceable to man : 

The first great step was Faraday's success in constructing 
an apparatus in which the action of lines of force produced 
continuous motion. 

The second step was the grand thought proved to be correct 
by experiments, that this production of motion by an electric 
current in a magnetic field might have its counterpart in the 
induction (production) of an electric current by the motion 
of a wire near a magnet. 

The third step was the establishment of 
- the fact that electric pressure will be 
m £ I induced in a wire moved in a magnetic 

J field only when it is moved so as to cut the 



lines of force. 
M The fourth step was the discovery that a 

change in a magnetic field induces a cur- 
FlG 26 rent in a conductor under its influence, just 

as a change in the current brings about a change in a mag- 
netic field near it. 

79. Fig. 26 is a diagram of Faraday's apparatus, showing 
the copper wire (C) so bent and hung, with its lower end 

*Joseph Henry, American physicist, secretary of Smithsonian Institution. 
Died 1878. See page 29 concerning Faraday. 

ioo 




ELECTRICAL ENGINEERING ^Q| 

immersed in a cup (M) containing mercury, that it rotates 
around the pole of the permanent magnet (N) continuously, 
when the current is turned on. It was a magneto, or magneto- 
electric generator, as it had a permanent steel magnet. 
Faraday also made the first dynamo : a copper disk revolving 
partly between the poles of a strong horseshoe magnet, and 
copper brushes collecting the electricity. In the first com- 
mercial small dynamos made, revolving coils of wire were 
substituted for the copper disk. 

Induced pressure 

80. If a coil of insulated wire is placed in circuit with a sen- 
sitive galvanometer, and the north pole of a strong bar magnet 
is suddenly thrust into the helix, the needle of the galvano- 
meter will be momentarily deflected, showing that a current 
flows in the direction opposite to that in which the hands of a 
watch move. If the bar magnet is withdrawn, a momentary 
deflection to the opposite side takes place. Our earth being 
a magnet, a long wire stretched out and suspended so that it 
may be swung sideways and thus cut the terrestrial lines of 
force, will set up a current strong enough to deflect the needle 
of a sensitive galvanometer to both sides of the zero mark, 
as it swings back and forth. 

RULE 30.— When a straight wire cuts 100,000,000 lines 
of force at right angle in every second of its motion, an 
electric pressure of one volt is produced. 

Of course, the rate at which the conductor cuts lines of 
force depends on several circumstances, viz. 

the number of lines of force in each sq. inch or cm., 
the length of the conductor in the field, 



102 MODERN ELECTRICITY 

the speed at which the conductor moves, and 
the angle at which it cuts the lines. 

It is evident that at right angles the conductor will cut the 
largest number of lines in a given time. 

EXAMPLE 38. 

In a wire, cutting 50,000,000 lines of force at right angles 
and at a rate of 50 times per second, a pressure of 25 volts is 
set up. 

(50 X 50,000,000 -*■ 100,000,000.) 

If the average alternating pressure induced in a secondary 
coil having 1000 turns amounts to 250 volts, then a secondary 
coil having 200 turns will supply 50 volts under the same 
circumstances. 

If the conductor is a coil of wire around the field of force, 
and if the face of the coil is at right angles to the lines of 
force, then each half of the coil will cut all the lines twice in 
one revolution 

EXAMPLE 39. 

A single coil of above description, including 2,500,000 lines 
of force, and turning at the rate of 40 revolutions per second, 
will develop a pressure of 4 volts. (4 X 40 X 2,500,000 h- 
100,000,000. We must multiply by 4, because the two halves 
of the coil cut the lines twice each in every revolution.) 

A coil of several turns must be considered a row of single 
coils connected in series, which we may compare to a Voltaic 
pile or a battery of cells connected in series. The E. M. F. 
set up in the coil equals the sum of the pressures developed 
in all its turns. 

Assuming the direction in which a wire moves to be straight 
ahead in front of a person (A), and the direction of the lines 



ELECTRICAL ENGINEERING 



103 




Figs. 27 and 28. 



of force vertically downwards (B). then the current flows from 
right to left in the wire C, ( See fig. 27, representing a slider 
C moving in the direction A on rails. 
The circuit consists of slider, rails 
and crosspiece D.) This is easily 
remembered by holding out the right 
hand in the manner shown in fig. 
28. The first or index finger repre- 
sents direction A, the second or 
middle finger direction B, and the 
thumb direction C. This agrees with 
Ampere's rule, as stated in § 70. 

Alternating current 

81. If a single wire ring is moved straight across a uniform 
magnetic field, it does not set up a current, because the 
E. M. F. in each half of the ring balances or neutralizes that 
in the other half. But if it is mounted on an axis so it may 

be revolved in 
the field, then 
the two halves 
cut the lines in 
opposite direc - 
tions during the 
two halves of 
each revolu- 
fig. 29. tion ; this pro- 

duces a current around the ring during each half revolution, 
but at the moment each half enters into the second half of 
the revolution, the direction of the current is reversed. A 
continued revolving, therefore, produces an alternating current. 



<r 



<m& 




<&m 




^^ 



104 MODERN ELECTRICITY 

Fig. 29 shows the same coil in the two positions during and 
after one half revolution. The large arrows indicate the 
direction of the lines of force, the short arrows show the 
directions of the currents. 

Induction coil 

82. It is immaterial whether the conductor moves through 
a stationary magnetic field, or whether a magnet moves about 
a stationary conductor; the result is the same. Furthermore, 
the magnetic field may surround a magnet, or a charged 
wire ; in either case a current will be set up in a conductor 
cutting the lines of force. If a small charged coil is thrust 
into the hollow of a larger coil, a current will flow in the 
larger coil during the time of moving ; as soon as both coils 
are at rest in respect to each other, the current stops ; while 
either coil is removed from the other, a current in the op- 
posite direction flows. In this case the charged coil, which 
may also be the larger one, is called the primary coil, and 
the other the secondary. If the two coils are fixed to each 
other, any increase or decrease of the current in the primary 
coil also sets up a current in the secondary coil ; this induced 
current lasts during the time of increasing or decreasing. 

This action of two coils upon each other is called mutual 
induction, and the two coils together are termed induction 
coil. The effect of an induction coil is greatly enhanced, if 
it surrounds a core of iron wires. If the core were made of 
solid iron, local currents would be set up in the iron which 
would cause heating and loss of power. (Compare §37.) 

The relation of the E. M. F. in the secondary coil to that 
in the primary, depends upon the number of turns and the 
size of wire in both windings. If the primary coil has compara- 



ELECTRICAL ENGINEERING 



105 




<S£C6MM*Y 

\ u u u u l 




t) V V V V V VIV V 



Co*f 
* /Mr£RR(/PT£# 






COrt££NSE/i 

Fig. 30. 



tively few turns of thick wire, and the secondary has many of 
very fine wire, a difference of potential between the two may 
be produced so great that the electrical discharge will leap 
across an air space of several inches ; the efficiency of such 
apparatus is usually rated by the length of spark they produce. 

They are much used in 
producing Hertzian waves 
for wireless telegraphy and 
in X-Ray work. Fig. 30 
is a diagram of a ruhm- 
korff coil. The core of 
the primary, wound 6 
turns, operates as a cir- 
cuit breaker by attracting 
a little armature mounted 
on a spring which nor- 
mally presses against the point of a screw, closing the primary 
circuit. Of course, the moment the circuit is broken, the 
core loses its magnetism, and therefore releases the armature, 
only to attract it again immediately, because the moment 
the armature is in contact with the screw again, the current 
starts flowing. Thus the circuit is "made" and "broken"' 
very rapidly and automatically, by the interrupter. 

Self=Induction ; Lenz's law 

83. At every "make" the field of force of each turn in the 
coil grows rapidly, and cuts the neighboring turns, inducing an 
E. M. F. that opposes the increase of the current. On the 
other hand, at every "break" the primary field rapidly 
vanishes, the lines again cutting the turns, but in a manner 
that tends to oppose the decrease of the current. This self- 



106 MODERN ELECTRICITY 

induction may be considerable, according to the number of 
wires; spark coils used to light the gas, etc., are based on 
this principle ; they may be supplied by a single cell. Ruhm- 
korff added to the apparatus a condenser (See fig. 36), con- 
nected in parallel with the interrupter. It takes up the self 
induced currents, thus making a quicker break. 

Induction coils transfer power from one circuit to another 
by the effect of magnetism, but without any electrical connec- 
tion. They are a means, therefore, of converting energy, and 
here, as everywhere in such cases, the 44 input " must be 
larger than the required "output" by a percentage high enough 
to allow for the inevitable loss by conversion of energy into 
heat, by leakage, etc. A transformer, or converter, is an 
application of the induction coil. 

The directions of magnetic fields and induced currents, as 
mentioned throughout the preceding paragraphs, may be stated 
in this general law : 

RULE 31 . — The magnetic field of a current induced by a 
change in a magnetic field, opposes this change, and 

The direction of an electric current induced by the movement 
of a conductor is such that its effect opposes the movement. 

This law was first formulated by a German scientist, Lenz. 

Questions and Answers. 

Q. What is induction density ? 

A. The number of lines per square unit (inch or cm.) 

Q. What is total flux? 

A. The total number of lines of force. 

Q. What causes the sparks in a spark coil? 

A. Self induction of the many turns of the coil. 



CHAPTER VII. — Meters and Measurements 

Electrical units 

84. At a meeting of electricians at Paris in 1881, an 
absolute system was agreed upon, the bases of which are the 
centimeter, gramme and second. (C. G. S. units.) 

TABLE OF ELECTRICAL UNITS. 



Unit of 



Strength . . 

Quantity. 
E. M. F... 

Resistance 

Capacity. . 
Power 



Work 
Heat 



}•• 



Sym- 
bol. 

I 


Name. 


ampere 


coulomb 


9 


volt 


E 


ohm 


R 


farad 


C 


watt 


w 


joule 



Relation to 
other units. 



volt -r- o*hm 

ampere xsecond 
ampere x ohm 

volt -f- ampere 

coulomb -4- volt 
volt x ampere 

f volt X coulomb 
{ amp. 2 x sec. 
X ohm 



Value. 



C G. S.> 



icr 

IO 
IO 8 

io 9 

IO" 

IO 7 



IO 7 
IO 7 



-1 



Equivalent. 



0000105 gr. hydrogen 
liberated per second. 

•926 standard Daniell 
cell. 

106 cm. mercury. 1 sq. 
mm. cr. section at 0° C 

•0013405 or ^ H. P. 
746 

•7373 foot pound. 
•238 calorie. 



*td1 = 



io 1= io; io-=ioo; io 3 =iooo; io 6 = 1,000,000 ; 



io°=i ; 



I0 " 1 = i5 =01 5 io- 2 =752=o-oi; 10^=— 3 =o- 



I 

,-6= r = 



001 ; io -v = ^yj=o.oooooi. 

A volt is the E M. F. which maintains a current of one 
ampere through a resistance of one ohm. 

A farad is the capacity of a body to be charged to a, 
potential of one volt by one coulomb. 

An ampere is the strength of a current which is produced 
by the pressure of one volt against a resistance of one ohm ; 
:>r which conveys one coulomb per second. 

107 



-[08 MODERN ELECTRICITY 

An ohm is the resistance of a column of mercury 106*3 cen- 
timeters in length, having an area of one sq. millimeter, at 
0° C, or 32° F. (International or legal ohm.) 

A coulomb is the quantity of electricity conveyed by one 
ampere in one second. 

A joule is the work done in one second by one ampere 
passing a resistance of one ohm. 

A watt is the power of a current of one ampere under a 
pressure of one volt, which equals one joule per second. 

Classification of electric meters 

85. It is evident that the strength of an electric current 
employed, whether infinitely small or of enormous magnitude, 
should be known, to assure safety and accuracy. Instruments 
for measuring currents are called amferemeters or ammeters. 
There are also milk 'amperemeters When used, they are con- 
nected in series in the circuit. Physicians measure a current 
by milliamperes (one thousandth part of one ampere) ; in the 
telephone service microamperes (one millionth part of one 
ampere) are used. 

If the electrochemical effect of the current is utilized in 
this instrument, it is called a voltameter. 

Most amperemeters take advantage of the magnetic effect 
of the current, while some make use of its heating effect. 

Of magnetic amperemeters there are several classes : 

Some use soft iron parts moved by magnetism ; in others 
a permanent steel magnet is acted upon or acts ; in others 
one of two coils move by the force produced by the mutual 
action between them. The first two classes mentioned are 
galvanometers, the third class are electrodynamometers. 



ELECTRICAL ENGINEERING JQ9 

Alternating currents cannot be measured by amperemeters 
of the second class, because the moving parts would be moved 
first in one and then in the other direction, and with a 
rapid alternation would stand still. Instruments having a soft 
iron core built up of thin parts serve well in this case, 
because it is always attracted by a current. Such a core is 
called a magnetic vane, Electrodynamometers can be used 
for alternating currents, as the current reverses at the same 
moment in both coils. 

Voltameter 

86. A voltameter measures currents by their electrochemical 
action. In § 50 the water voltameter has been fully described 
and explained. In all voltameters the cathode and anode 
are made of the same metal, so that the cell does not set 
up a current of its own. 

metal voltameters are made of copper, tin or zinc electrodes 
in a solution of the salts of the same metal. The electric 
current decomposes the solution, the metal part is deposited 
on the cathode, and the acid part attacks the anode, form- 
ing a new portion of the solution. The quantity deposited 
on the cathode is generally taken as the measure of the 
current. The solution for copper generally used is copper 
sulphate of a certain strength, for amalgamated zinc plates 
(see § 37) a zinc sulphate solution, for tin plates a tin 
chloride solution, etc. In a silver voltameter a solution 
of nitrate of silver is used, acting upon a plate of pure silver 
and depositing on a platinum plate. The international ampere 
% (see § 48) is determined by means of a silver voltameter. 
In the table of equivalents (page 53), under the heading 
of u Electrochemical equivalent in milligrammes per cou- 



HO MODERN ELECTRICITY 

lomb," the quantities deposited in one second by a current of 
one ampere are given for all substances of importance in this 
connection. 

EXAMPLE 40. 

If a current of 3 amperes flows for 15 minutes through 
a silver voltameter, 3-0186 grammes of silver will be depos- 
ited. (3X15X60 = 2700; 2700 X -001 1 18 = 3-0186) 

EXMPLE 41. 

If 12 grammes of cupric copper are deposited on the 
cathode of a voltameter in 90 minutes, the current will 
be 6-74 amperes. (12-^- -000327 =36,697; 36,697 ~- (90 X 

60) =6-79). 

Galvanometer 

87. A galvanometer measures currents by their magnetic 
effect. It consists of a magnetic needle, pivoted at the 
center of an electric coil, and a scale showing the angle of 
deflection. According as the coil has many fine turns and 
few coarse ones, the galvanometer will be more or less sen- 
sitive. Any common galvanometer is most sensitive when 
the coil is at right angles to the magnetic meridian. Some 
galvanometers have their needles made independent of the 
earth's magnetism by means of an adjustable controlling 
magnet, and if the meter is to serve for very delicate work, 
astatic needles are used, consisting of one or more groups 
of 2 similar magnetic needles fastened to a thin light wire 
one above the other, and their north poles pointing in opposite 
directions. ("Astatic" means "not tending to assume a 
fixed position".) For the purpose of the galvanometer, even 
an agate or crystal pivot of the needle would offer too much 
friction; the needle is, therefore, usually fixed to a delicate, 



ELECTRICAL ENGINEERING 11] 

but strong fiber. The needles have shapes of great variety; 
a common form is composed of several parallel small mag- 
nets fastened on a disk. 

In some kinds of galvanometers the deflections bear a 
fixed relation to their cause, the currents. This relation is 
called a constant, ( resistance of circuit indicated by a 
deflection of one scale divisions). An instance is the sine 
galvanometer, in which the trigonometrical sine of the angle 
through which the coil is moved by the current, is pro- 
portional to the current. In the tangent galvanometer, 
the trigonometrical tangents of the angle through which the 
needle is deflected by the current, is proportional to the 
cause, the current. In other kinds the relation must be 
established by actual experiments with currents of known 
strength. The results of such experiments are then entered 
on cross ruled paper in the shape of a calibration curve. 
Other kinds to be mentioned are mirror or reflecting 
galvanometers, differential galvanometers, etc. (See §93.) 

Ammeters may be so calibrated that their indications read 
directly in volts instead of amperes. In this case they are 
called voltmeters. The coil in an amperemeter has a few 
coarse turns, for measuring current, while that in a voltmeter 
has many fine turns, for measuring pressure. Weston's 
voltmeter is a galvanometer, with a permanent steel mag- 
net, and a moving coil mounted on pivots and carrying a 
pointer playing over a scale. 

88. When a sensitive galvanometer is to be employed for 
very strong currents, it is necessary to shunt it. The shunt 
ing is generally done with a view to having a unit ratio 
between the two parallel currents, such as -J, -£-$, or 7 | 7 etc., 



112 MODERN ELECTRICITY 

and this is obtained by making the shunt resistance nine> 
ninety-nine, or nine hundred-ninety-nine times that of the 
galvanometer. A shunt box, providing these resistances by 
the simple insertion of one or more plugs into their proper 
holes, is generally sold with each galvanometer. 

EXAMPLE 42. 

When a galvanometer having a constant of '00005 ampere 
per division, reads 100, when shunted by a -^ shunt box, 
a current of 0-5 ampere is flowing. 

( 1 00 X 1 00 X -00005 = 1 0,000 X -00005 =0-5 ampere. ) 

Electrometer 

89. The electrometer is an instrument for measuring the 
attraction between two bodies, one charged with a high pres- 
sure, and the other charged with a low pressure, the deflection 
of the needle showing the difference of pressure. Such an 
electrostatic voltmeter is much in use for everyday 
measurements of electric pressure in light and power stations. 
It may also be used for measuring the difference of potential 
between a charged body and the earth (zero), or between the 
two plates of a condenser. The quadrant electrometer is 
so called, because the principal part of it resembles a cylin- 
drical box, divided into four wedges or quadrant?, of which 
each pair of opposite quadrants are connected and charged, 
one pair positive, the other negative. 

An electric pressure may also be measured by connecting a 
part of the resistance with a small battery of known pressure 
and a galvanometer in series, in such a way that the two cur- 
rents flow in opposite directions. 



ELECTRICAL ENGINEERING H3 

EXAMPLE 43. 

If the battery is of 1-4 volts, and the galvanometer indi- 
cates zero, when the T7 \ 7 part of a total resistance of 
50,000 ohms is connected, then the voltage in the -joVe" 
part balances the pressure of the battery, and this pressure 
of 1-4 volts must be to the unknown pressure, as 1000 is 
to 50,000. 

1-4X50,000-5-1000 = 70 volts. Ans. 

Such cells, constructed with a special view to serving for 
measuring pressure by comparison, are called standard cells. 
The Chicago Electric Congress, 1893, recommended Clark's 
cell, the pressure of which is 1-434 volts at 15° centigrade. 

Electrodynamometer 

90. The Siemens electrodynamometer has a movable 
coil suspended at right angles around a fixed one. The ter- 
minals of the movable coil are immersed ( below the fixed 
coil) in mercury cups which close the circuit. The tendency 
of the movable coil, when a current is flowing, to place itself 
parallel to the fixed one, is counteracted by a spring regulated 
by a thumbscrew, torsion head. The pointer of this torsion 
head indicates, on a scale, an amount proportional' to the 
square of the current, because the current flows through the 
two coils, and the coils act on each other mutually. 

In the kelvin balance, the tendency of two parallel coils 
to approach each other, is directly balanced and indicated 
by means of a slider on a scale beam. 

Rheostat 

91. The rheostat is a collection of resistances of various 
known heights, through any or all of which the operator may 
cause a current to flow at one time. It consists of a box 



-3-3- 



tnj 



H4 MODERN ELECTRICITY 

holding a number of spools wound with various lengths and 
sizes of insulated wire, mostly of German silver or other 
alloys of high resistance and small tempera- 
ture coefficient. Each wire is doubled up, 
to prevent self-induction, wound on a spool 
and immersed in paraffine. The spools are 
bolted to the inside of the box cover. The 
wire ends of each spool are connected to 
two brass blocks fastened on top of the cover. These 
blocks are placed in such a way, that by inserting a plug 
between a pair of blocks one spool is short-circuited. Each 
block being connected to two spools, all the spools are con- 
nectedin series when no plugs are inserted. (See diagram . 
fig. 31.) Thus the resistance of anyone coil or number of 
coils may be cut out by inserting the proper plug or plugs. 
The resistance of the plug is negligible, that is, so small that 
it may be disregarded. The wires are selected to furnish a 
set of resistances that have a certain ratio, generally a 
decimal one: y-Q-Q' iV» '• 10» 100, etc., ohms, and the final 
adjustment of all the coils requires great skill. But even 
with the most perfect rheostat it is necessary to make allow- 
ance for the temperature at the time of measuring, when 
great accuracy is aimed at. 

Wheatstone's Bridge 

92. The coils for the rheostat are tested by means of an 
apparatus named after the English scientist Wheatstone, the 
inventor. Fig. 32 illustrates its principle. A, B, R are rheo- 
stats, X is the coil to be measured, G is the galvanometer. 
if key 1 , near the battery, is depressed, the current flows to 
point O where it divides, to meet again at N and to return to 



ELECTRICAL ENGINEERING 



115 



the battery. The plugs of the rheostats are set in such a way 
that the difference of pressure between the two points O and 
N by way of M equals that by way of P. If this difference 
is called E, then the resistance (always proportional to the fall 




of potential ; see § 58) between points M and TV ( called b ) 
x 



equals E 



where x represents the resistance of X, 



x + b' 

the coil to be tested, and b the resistance of the rheostat B. 
A and B are set at the same resistance, and then the key 
2 near the galvanometer is pressed. If the pressure in X is 
greater than in R, a current will flow from M to P, indicated 
by the galvanometer. If the pressure in R is greater, the 
galvanometer needle will be deflected in the opposite direction. 
Then the plugs of R are manipulated until the bridge is 



116 MODERN ELECTRICITY 

balanced, that is, until the galvanometer shows no current 
between M and P. 

By varying the ratio of resistance between A and B from 
1 4- 1 to 1 -h 10, 1 ^- 100 etc., the work is greatly facilitated, 
because, when the bridge is balanced, the resistance of X is 
to that of B, as that of R is to that of A. 

~ br 

x '. b : : r : a. Or, x = — - . 

a 

EXAMPLE 44. 

a. R reads 350, A 100 and B 10, when the bridge is bal- 
anced. What is the resistance of X? 

1 X 350 -*- 100 = 35 ohms. Ans. 

b. What resistance should be given to R, A and B, to 
measure 836,500 ohms ? 

836,500: 1000::8365: 10. R 8365, B 1000, A 10. Ans. 

A simple form of Wheatstone's bridge is the divided wire 
bridge, used especially for measuring a low resistance by 
another known resistance. In this instrument the connection 
with the galvanometer key is not fixed, ( as at M in fig. 
32), but contact may be made at any point of a wire stretched 
along a graded scale, from which the ratio of the two parts 
of the wire ( which is the same as that between the known 
and the unknown resistance) may be read off. 

Insulation resistance 

93. Very great resistances, like the insulation resistance (of 
insulated wires) between wire and ground, are measured by 
means of a delicate reflecting galvanometer with shunt box 
and a portable testing battery, usually made up of 50, 100 or 
200 silver chloride cells. The battery, galvanometer and 
unknown resistance are connected in series ; the deflection of 



ELECTRICAL ENGINEERING 



117 



the galvanometer is then compared with its deflection at some 
standard resistance, usually from 25,000 to 1,000,000 ohms; 
the resistances are in the same ratio. 

Suppose a powerful testing battery of 200 silver chloride 
cells and a standard (known) resistance of two megohms ( 1 
megohm = 1 million ohms ), connected up in series with a 
fine galvanometer shunted by the ^ shunt. If the galvano- 
meter under these circumstances gives a deflection of 60 
scale divisions, then 60 x 100x2=12,000 would be its 
constant, that is to say, if not shunted, it would indicate 12,000 
megohms by a deflection of one scale division. If an unknown 
resistance, as the insulation resistance of a mile length of 
electric light cable, is to be measured, the cable is substituted 
for the known re- 




9 



sistance, one end 
being grounded. 
If then the gal- 
vanometer, not 
shunted, shows 
4 scale divi- 
sions, this will in- FlG * 33 * 
dicate the insulation resistance to be = ^ X 12,000 = 300 
megohms, because insulation resistance is the reverse of 
insulation conductance. (See § 53. ) A length of 3 miles of 
the same cable would have an insulation resistance of 100 
megohms, because the single miles with their paths of leakage 
are in parallel. 

Hot wire instruments 

94. Fig. 33 is the diagram of a simple instrument for 
measuring a current by means of the expansion of a wire by 



l\S MODERN ELECTRICITY 

heat. The apparatus is, of course, carefully enclosed, to 
avoid the effects of air currents. The wire is fastened at one 
end to a metal wheel through which the current passes to one 
of its supports and to another wire, closing the circuit. The 
wheel carries the pointer, and is pulled around one way by the 
spring F, when the temperature of the wire is increased by 
the increasing current, and it is pulled around the other way 
by the wire, when the temperature decreases. 

The Cardew voltmeter, named after its inventor, is based 
on the same principle. It uses a platinum-silver wire, 25 
ten-thousandths of an inch in diameter, and measures up to 
120 volts. 

As the direction of the current is immaterial, hot wire 
ampere meters can be used to measure alternating currents. 

Wattmeter 

95. In these instruments there is a fixed coil (current coil 
in series) and a movable coil (pressure coil), the two forming 
separate circuits. The fixed coil, wound with a thick wire of 
low resistance, carries, when connected, the amperes of the 
current ; the movable coil is wound with a thin wire of 
high resistance (as in voltmeters) to receive a current propor- 
tional to the volts. When in use, the movable coil of the 
wattmeter is connected, by means of binding posts, across the 
terminals of the machine, as a shunt, and the fixed coil is 
connected in series to the circuit, the power supplied to which 
is to be measured. Then the entire current has to flow 
through the thick wire of the stationary coil, while only a part 
of the current flows through an auxiliary resistance and 
through the thin wire of the movable coil. Thus, the mag- 
netic effect of the fixed current coil being proportional to the 



ELECTRICAL ENGINEERING 



119 



amperes, and that of the movable volt coil being proportional 
to the volts, the indications on the scale will be proportional 
to amperes times volts = watts. 




Some wattmeters have a set of dials like a gas meter, 
indicating the total number of watt hours (watts times hours) 
used. They are called recording or integrating (adding) 
wattmeters. See fig. 34. In these the volt coil is arranged 
as an armature (revolving part), while the current coil forms 



120 



MODERN ELECTRICITY 



^TTTT 



3m 



Si 



the fixed magnetizing windings around it, so that the appa- 
ratus resembles a small motor. The speed of the revolu- 
tions of the armature is retarded by strong permanent 
magnets, between the poles of which a copper disk connected 
with the axis of the armature revolves, thus setting up electric 
currents which cause attraction by the magnets. Fig. 35 is a 
diagram of the manner of connecting a wattmeter (W) with 
a circuit. CC are the connections with the current coil, 
VV those with the volt coil. L indicates the lamps. 

Others are arranged to show ampere hours ; and they are 
called coulomb meters, because an ampere second means 

the flow of one coulomb of 
electricity. By multiply- 
ing the indicated ampere 
hours by the average 
pressure, the watt hours 

are found. 
Capacity of condensers 

96. From what has been said about the nature of a con- 
denser (see § 19), it is evident that any two conductors lying 
close together, unless separated by a well insulating dielectric, 
will increase their capacity, acting inductively on each other 
and modifying their relative potentials. 

Because of its high specific inductive capacity (see 
table in §99), it is not advisable to use a good insulating 
material like glass for continuous insulation of wires and 
cables. 

Condensers are usually mounted in bases of Ruhmcorff's 
induction coils to lessen the inverse current at the " make " 
and to increase the direct electro-motive force at the 



Fig. 35. 



ELECTRICAL ENGINEERING 121 

"break." The sparks of induction coils thus equipped are 
longer and only pass one way. 

It is clear that the charge of a condenser must vary directly 
with the capacity, and, as the capacity of a water tank 
increases with increasing height, similarly the charge of a 
condenser also varies directly with the pressure. Therefore, if 
the capacity is fixed, the charge is proportional to the pres- 
sure ; and if the pressure is constant, the charge is proportional 
to the capacity. A microfarad is one millionth of a farad ; 
hence : 

RULE 32. — C (capacity in microfarads) = 1 ,000,000 X Q 
(quantity on each plate in coulombs) divided by E (pressure 
in volts). 

„ 1,000,000X0 _ 1,000.000 XQ - EXC 
C= ^ tr — (u — 



C 1,000,000 

EXAMPLE 45. 

a. If a condenser is charged with -0002 coulomb, and the 
difference of potential is 10 volts, the capacity is 20 micro- 

famds ' 1, 000 ,000 X -0002 

C= = 100 X -2 = 20. 

b. A condenser of 2*5 microfarads capacity requires a 
pressure of 2,400 volts to charge it with -006 coulomb. 

^ 1 ,000,000 X -006 6,000 



2-5 2-5 



2,400. 



c. If a condenser of 10 microfarads capacity is charged by 
a difference of pressure of 50 volts, the quantity of the 
charge is -0005 coulomb. 

1,000,000 10,000 



122 MODERN ELECTRICITY 

Arrangement of condensers 

97. Condensers usually consist of alternate layers, of equal 
size, of conducting sheets (as tin foil) and dielectric sheets 
(as mica, wax paper, or oiled silk). The adjacent layers of 
tinfoil are charged with opposite kinds of electricity, one posi- 
tively, one negatively. The connection between the several 
plates will depend on the use to which the condenser is to be 
put. Its capacity is directly propor- 
tional to the area of the plates, and 
therefore, in order to have their 
total capacity equal the sum of 
their individual capacities, they are Fig 36 

connected in parallel. (See fig. 36.) 

If on the other hand, it is the object to use the smallest 
possible capacity of the condenser, they are connected in 
series, which arrangement makes the total capacity equal to 
that of one condenser divided by the number in series, 
because in this the thicknesses of all the dielectric sheets 
must be added together. 

When several condensers of different capacities are joined 

a) in parallel, they will simply act as a large condenser of a 
capacity equal to the sum of capacities of all the condensers. 

b) in series, the total capacity will be the reciprocal of the 
sum of the reciprocals of the capacities of all the condensers. 

EXAMPLE 46. 
3 
6 condensers of 1*5 ( = ^) microfarads 

(a) in parallel, 6X 1*5 = 9 mf. Ans. 

(p) in series, 6 times the reciprocal of - ; 

2 12 
6X- = -=-= 4. The reciprocal of 4 = \ mf. Ans. 



ELECTRICAL ENGINEERING 123 

EXAMPLE 47. 

Three condensers of ^, £ and £ microfarads, connected in 
parallel, have a total capacity of 1 microfarad. If in series, 
the combined capacity is T \ microfarad. 

tt + ^+i = l; 3 + 2 + 6=11.) 

By arranging 2, 3, 4 or more condensers in all possible 
combinations, as in parallels of 2 or 3 sets of series of 3 or 2 
etc., a large variety of capacities can be obtained, as is the 
case in the standard condenser box. 

Testing a condenser 

98. In testing the capacity of an insulated wire or cable, a 
standard condenser of nearly the capacity of the wire is 
chosen, charged by a small battery, and then connected so as 
to discharge through a galvanometer, which will show a throw 
of the needle in proportion to the quantity of electricity dis- 
charged. The one end. of the wire is connected with the bat- 
tery, the other with the earth and the same two operations are 
carried out. As the pressure is the same, the two capacities 
(of the standard condenser and the wire) are in proportion to 
the quantities, and also in proportion to the throws. In speak- 
ing of the capacity of an insulated wire or cable, it must be 
remembered that it is considered a condenser in this case, the 
insulated wire forming one plate, the earth or return wire the 
other plate, and the insulation the dielectric. 

In a similar way the pressure in a condenser is measured 
by means of an electrometer or electrostatic voltmeter. It 
cannot be measured with an ordinary voltmeter. 

99. In the following table the inductive capacity of a 
number of substances is compared with that of air, which 
being the lowest, is taken as the unit (one). 



124 MODERN ELECTRICITY 

TABLE OF SPECIFIC INDUCTIVE CAPACITY. 



DIELECTRIC. 



Vacuum, .... 
Oxygen, .... 
Air at o° C. and 760 mm 

barometric pressure, 
Carbonic acid 
Pitch, . . 
Paraffine, 
Turpentine, 
Ebonite, 
Rubber, . 
Benzol, . 
Gutta percha, 



CAPAC- 
ITY. 



0-9985 
0-999674 



1*000356 
i-8 
1-68-2. 

2*2 

I-9-3 48 
2*12-2 69 

2*3377 
3-3-4-9 



DIELECTRIC. 



CAPAC- 
ITY. 



Resin, .... 
Sulphur, 

Sulphureted carbon, 
Kerosene, . 
Shellac, .... 
Castor oil, . 
Glass, .... 
Mica, .... 
Iceland spar, . 
Selenium, 
Alcohol, .... 
Water, .... 



2-48-2-57 
2-2-3 9 
I -0023 
2-69-2 8 

2-74-3 73 
4-61-4 8 
2-8-9 9 
4-6-8 
80 

10*2 

24-27 O 

80 



Questions and Answers. 

Q. How does a voltameter differ from a voltmeter? 

A. A voltameter is used to measure electric currents by 
means of their electrochemical action. A voltmeter measures 
electric pressure, mostly by means of electromagnetic action. 

Q. Is an electromagnetic voltmeter a milliamperemeter ? 

A. It is ; only it is graduated to read in volts instead of 
amperes. 

Q. What is the use of the spring in a simple ampere- 
meter ? 

A. If it were not there, the smallest amount of electric cur- 
rent would draw the iron core completely into the coil. 

Q. How is a voltmeter coil wound? 

A. With many turns of very fine wire. 

Q Is the Siemens electrodynamometer a wattmeter ? 



ELECTRICAL ENGINEERING 125 

A. No ; generally it is arranged to serve as an ampere- 
meter, giving the square of the current, while a wattmeter 
indicates the watts product of current and pressure. 

Q. Of what service is a recording wattmeter in a railway 
switchboard. 

A. By its use it becomes possible to know exactly how 
many electrical H. P. hours are consumed each day. 

Q. Describe the Cardew Voltmeter ? 

A. It is a very delicate instrument. The two ends of the 
platinum wire (of 0-0025 inch or 2\ mils diameter) about 4 
yards long, are fixed to two small brass blocks, near together, 
then the two lengths of wire are laid around two small grooved 
wheels fixed one yard below, and are returned to a point 
between the brass blocks, where the wire is laid around one 
small insulating grooved wheel This wheel is pivoted on a 
brass strip, which is connected with a spiral spring above by 
means of a fine platinum wire that is straight except that it 
makes one turn around a small pulley. The pulley is geared 
to a toothed wheel which carries a long pointer playing over 
a scale. The spiral spring holds the wires taut and is adjust- 
able at the top of the instrument, by means of a thumb screw, 
so that the pointer can be set at zero at the beginning of a 
test. When the connections are made by means of the two 
brass blocks, the current passes only through the four yards 
of platinum wire. The two loops of wire (of 2 yards each) 
are heated by the current and expand alike, so that the spiral 
spring decreases in length, and the pulley turns. Even the 
slightest turn of the pulley will cause a considerable deflection 
of the long pointer. A hair spring presses the gearing of wheel 
and pulley together, so as to insure perfect action. 



CHAPTER VIII. — The Direct Current Dynamo 



ioo. After Faraday's discoveries, stated in §78, improve- 
ments were made by various scientists, especially Siemens 
and Gramme, until by the year 1860 the dynamo became 
practically what it is to-day. aside from minor additions. 

The alternating current produced in a coil revolving between 
the poles of a magnet (compare fig. 29) may be collected by 

two rings, each of which is 
connected with one end ter- 
minal of the coil, and by 
means of sliding brushes 
passes from the rings into 
the external circuit which 
may consist of lamps, 
motors or other apparatus 
which consume the cur- 
rent. By splitting the ring 
into two half-cylinders, and 
by insulating these halves 
from each other and from 
the shaft of the revolving part (see fig. 36) and by setting the 
brushes so that they are exactly opposite each other and 
never rub against more than one half of the ring, or seg- 
ment, the alternating current is changed or commutated 
into a continous or direct current. One of the brushes is 
always kept positive and the other negative, the current 
flowing from the positive brush through the external circuit 

126 




Fig. 36, A. 




DIRECT CURRENT LOCOMOTIYE CRANE. 

Raises five tons 20 feet in one minute. 6 H. P. Travels 100 yards a 

minute. 30 H. P, E. M. F. no volts. 



127 



128 



MODERN ELECTRICITY 



back to the negative brush, and thence through the arma- 
ture coil to the positive brush. 

The brushes are usually mounted on a rocker arm, so that 
they may be nicely adjusted to the commutator segments, 
to avoid sparks, which would greatly injure the commutator. 

Armature 

101. The current is created by the wire cutting the mag- 
netic lines of force, extending from the north pole (TV) to 
the south pole (5). The effect is greatest when it cuts them 
at right angles (see §80). In the position of the wire 
shown in fig 36A,it moves, at least for a moment, entirely 
parallel with the lines of force. When it turns in the direc- 
tion of the lower arrow, the upper half moves toward 
the middle of TV, and the lower half moves toward the middle 
of 5, cutting the lines of force at an ever increasing angle, 
until both halves of the wire stand at the same level with 
the shaft. At this moment the lines of force are cut at 
right angles, and therefore the pressure produced is strongest, 
In the position shown in fig. 36A the pressure is 0. Thus a 
rise and fall of potential is produced 
during each half revolution. Because 
of this wavelike changeability, and 
because the commutation of large 
currents is impractical at the full 
pressure required by our industries, 
the one coil was replaced by Gramme, 
in 1870, by a number of coils, wound 
around a ring composed of iron wires, at equal distances 
from each other, and each connected with one of the equal 
number of segments of the commutator, on which two 




Fig. 37. 



ELECTRICAL ENGINEERING 129 

brushes are sliding. (See fig. 37.) The two brushes are set 
so as to take the current from the coils which at the moment 
are cutting the lines of force at the least angle. The current 
through the armature, from the negative to the positive brush 
flows in two paths, around each half of the ring, and this ten- 
dency is increased by the following interesting fact : The lines 
of force that strike the iron wire core of the armature, are 
deflected from their path because iron has a higher per- 
meability than any other substance ; they pass through the 
ring along the iron wire until they arrive at a point directly 
opposite the point where they entered, and then flow again 
in their first direction toward the negative pole. Conse- 
quently they are not cut by the wires lying in the inner 
hollow of the ring, but only by those on the outer circum- 
ference. This sets up pressure 
in two different directions, and 
both currents thus produced flow 
towards the positive brush. 

The principle of the Gramme 

Ring is also that of the Siemens 

Drum armature. (See fig. 38.) 

A drum is substituted for the ring and the coils are wound 

on the outside surface of the drum only. 

102. The Siemens drum is not made of one piece but 
is laminated, that is, made up of thin disks of sheet iron, 
insulated from each other, to avoid the so-called eddy cur- 
rents, set up in the core when it revolves in the magnetic 
field, cutting the lines of force. These currents would flow 
from one end of a solid core to the other, heating the core. 
It takes power to keep these currents flowing, and besides, 




130 MODERN ELECTRICITY 

the heat would injure the cotton and shellac insulation on 
the wire of the armature windings. The several disks of 
sheet iron are insulated from each other by layers of thin 
tissue paper or coatings of linseed oil, which prevent the 
flow of current from one disk to the next, but do not inter- 
fere with the passage of the lines of forces through the 
core. Lamination does not prevent all loss of power, how- 
ever. The armature of a running dynamo is always at a 
higher temperature than its surroundings, a sign that a part 
of the power supplied is lost somehow, probably by the 
resistance offered by the molecules to the reversing of the cur- 
rent at every half revolution. (Compare §81). The softer the 
iron or steel in the core, the smaller is this loss by hysteresis. 

RULE 33. — The loss of power by hysteresis and eddy cur- 
rents in any dynamo is proportional to the speed at which the 
armature revolves. 

The Magnetic Circuit 

103. The electromagnet between the poles of which the 
armature revolves, consists of the pole-pieces, of concave 
shape so as to embrace the armature, of the field cores, 
around which the wire is wound, and of the yoke, the part 
which connects the field cores. The current required to set 
up the magnetic field (exciting current), is usually furnished 
by the dynamo itself, even at starting, when the residual 
magnetism in the magnets is utilized. At the first start the 
current of a small battery, or of a magneto machine is used. 

The space between the iron of the magnet poles and the 
iron core of the armature is called the air space or gap, 
although partly occupied by the armature coil. This air 
space must be made as small as possible, in order to pre- 



ELECTRICAL ENGINEERING 13) 

vent immoderate leakage, principally due to the reluctance 
of the air space, and consisting in the going astray of mag- 
netic lines of force, which are apt to cause mischief, as by 
drawing iron nails or scraps into the air space, The smaller 
the air space, the smaller the magnetic force required, and 
the smaller, consequently, the number of ampere turns 
needed on the field cores of the electromagnet. To reduce 
the air space as much as possible, the surface of some cores 
is grooved parallel to the axis, and the coils placed in the 
grooves, which arrangement does away with almost all the 
gap, as the teeth ( iron core ridges ) between the grooves 
may all but touch the poles. 

104. The total reluctance of the magnetic circuit of a 
dynamo is the sum of all the reluctances of the yoke, field 
cores, pole pieces, air gaps and armature. The number of 
ampere turns on the field cores ( nc ) required to create a 
field of a given number of lines (TV) through a given reluc- 
tance (P), is calculated by means of the following formula 
(see §81): N p 

and the number of lines of force by the formula 

1-257 nc 



N = 



P 



EXAMPLE 48. 
The reluctances of the parts of a magnetic circuit are : 
field cores -0002 each ; pole pieces -0001 each ; yoke -0002 ; 
armature -0006 ; air spaces -0016 together. A current of 3 
amperes flows through the magnet coils, and the dynamo has 
2,000,000 lines of force. How many turns in the magnet 
coils ? 



132 MODERN ELECTRICITY 

Total reluctance = ('0002 X 2) + (-0001 X 2) + -0002 + 
•C006 + -0016= -003 

2,000,000 X -003 6000 

nC= L257 = T.257 =47?3 tUmS - AnS ' 



EXAMPLE 49. 

Each conductor of a one-coil armature of 25 ampere 
turns cuts 1 ,500,000 lines of force in each half revolution ; 
the armature makes 1200 revolutions per minute. What is 
the difference of potential between the brushes ? 

25 turns = 50 half turn conductors. Each conductor cuts 
the lines of force twice in each entire revolution. 2 X 50 = 
100. 1200 revolutions per minute = 20 rev, per second. 

100X 1, 500,000 X 20 = 3,000,000,000 lines of force per 

second. 100,000,000 lines of force cut per second make 1 

u .u r 3,000,000,000 ^ . 
volt, therefore ,^ ^^ ^^ = 30 volts. Ans. 
100,000,000 

EXAMPLE 50. 

) ,500,000 lines of force pass through a Siemens arma- 
ture having 40 coils of 6 turns each, and making 10 revolu- 
tions per second. What pressure is set up? 

Each turn cuts the lines of force, not four times like 
a single coil, but only twice, because in the Siemens armature 
each ampere turn has only one conductor that cuts the lines 
of force. Therefore : 

2 X 40 X 6 X 1 ,500,000 X 1 = 7 ,200,000,000 lines of force 

, 7,200,000,000 ^ . 
cut per second; t ^ ^^ ^^ =72 volts. 
K 100,000,000 

This pressure is divided between two paths in parallel : 

72 

— = 36 volts. Ans. 
2 

NOTE. — Under the same circumstances, 20 coils cf 6 
turns, or 40 coils of 3 turns each , would set up 36 volts. 



ELECTRICAL ENGINEERING 133 

EXAMPLE 51. 

A Gramme armature of 50 coils of 4 turns each, making 
20 revolutions per second, sets up a pressure of 100 volts. 
How many lines of force are in the field? 

100 volts in two paths = 200 volts. 

2 X 50 X 4 X 20 X x = 200 X 1 00,000,000 

200 X 100,000,000 



x = 



x = 



2X50X4X20 
20,000,000,000 



8000 
* = 2,500,000 lines of force. Ans. 

Classification of machines 

105. Dynamo-electric machines may be divided into classes 
according to 

1. the manner in which the magnetism of the field mag- 
nets is obtained, whether self exciting or separately excited. 

2. the form and number of their field magnets. 

3. the nature of their magnetic fields, whether uniform, 
alternating, symmetrical, dissymmetrical, pulsatory, reversing, 
or shifting. 

4. the shape of the armature, whether drum or disk, 
pole or radial, ring or spherical. 

5. the manner in which the windings of the field magnets, 
the armature and the external circuit are connected, whether 
series, shunt, or compound. 

6. the nature of the current obtained, whether continuous 
or alternating. 

Dynamo and Motor 

106. In a dynamo the armature is revolved by an engine 
or other means, and the revolutions of the armature coils, 



134 



MODERN ELECTRICITY 




cutting the lines of force of the magnetic field, set up a 
current in tne armature coils. In a motor, the electric 

current supplied by a dynamo 
or generator, or by a bat- 
tery, flows through the coils, 
of the field cores, setting 
Ml^fjQfiSB^ up a magnetic field, which 

FlGi 39. causes the armature to re- 

volve. Any direct-current 
dynamo may serve as a motor, if an electric current is 
sent through its field coils. The armature will revolve in 
a direction opposite to 
that in which it revolved 
when run as a genera- 
tor. The reason for this 
is that the mutual in- 
fluence of a magnetic 
field and a conductor 
operates, whether the 
conductor is moved in 
the magnetic field, set- 
tling up a pressure, or 
whether a charged con- 
ductor is placed in a 
magnetic field, generat- 
ing motion. (See §78). 
Generally speaking, the 
best dynamo will also make the best motor. 

Either the armature or the magnetic field may be made 
to revolve. (See §82.) Fig. 39 shows a stationary direct 




Fig. 40. 



ELECTRICAL ENGINEERING 



135 



current armature and fig. 39 its rotary magnetic field. Fig. 
41 represents a complete direct current generator of the 
most modern type. 




Fig. 41 



Various dynamos 

107. An iron clad dynamo is so called because armature 
coils are partly hidden from view, being embedded in grooves 



136 



MODERN ELECTRICITY 



or slots cut in the surface of the armature. The iron parts 
between the conductors are called teeth. In multipolar 
machines there is a double magnetic circuit, the lines of 
force dividing as soon as they enter the armature and passing 
back to the yoke through the two adjoining opposite poles. 
As they pass into the original pole from the yoke, their 
paths reunite. 

The name consequent-pole dynamo designates a machine 
in which the armature is placed between the field cores, so 
that the lines of force seem to lie, not between the pole 
pieces, but between two intermediate points. (See § 68.) 

108. In order to couple the dynamo directly to the engine 
shaft, inventors first constructed armatures of large diameters, 
so as to cut a great number of lines of force at low speed, and 
finally, they multiplied the number of poles from two to four, 

eight, twelve, etc. 
The two, four, six, 
eight (or more) 
couples of poles 
(jVand 5) are all 
set in one heavy 
yoke surrounding 
the armature. The 
poles are alter- 
nately TV and 5, 
and the magnetic 
currents pass from 
each N pole 
through the armature core to the two neighboring 5 poles, 
and on entering the yoke divide again in two currents towards 




Fig. 42. 



ELECTRICAL ENGINEERING 



137 



the two neighboring TV poles. These machines are called mul- 
tipolar in distinction from two-pole, or bipolar dynamos. 
(Fig. 42 represents an 8-pole dynamo.) As a rule, the number 
of brushes is equal to the number of poles, but by making 
proper cross connections between the commutator segments 
two brushes will suffice. 




Fig. 43. 



Series, shunt, compound 

IO9. In a SERIES WOUND DYNAMO 

the field circuit and the external cir- 
cuit are connected in series with the 
armature circuit, so that the entire 
armature current must pass through 
the field coils. (See diagram, fig. 43.) 

Series wound dynamos are used 
where a current of constant intensity 
is required, as in a series of arc lamps, 
because the magnetizing power of the 

winding increases with the increasing current. But where a 
constant potential is required, a series wound dynamo cannot 
be used, because an increase (or decrease) in the resistance 
of the external circuit (as by switching in or cutting out some 
arc lamps) will decrease (or increase) the E. M. F., from the 
decrease (increase) of the magnetizing current. An auto- 
matic regulating device is necessary to avoid these changes. 

A series wound dynamo will not sufficiently magnetize its 
own magnets until the armature has attained a certain speed, 
or unless the external resistance is below a certain limit. 
It is also apt to reverse its polarity, with disastrous con- 
sequences. 



138 



MODERN ELECTRICITY 









2^m 








lii 


lor 






t 


i 



Fig. 44. 



no. In a shunt wound dynamo (see diagram fig, 44) a 

field winding of high resistance is connected at the brushes 

in parallel to the external circuit, so 
that only a portion of the current gen- 
erated by the machine passes through 
the field winding, which consists of a 
large number of turns of very fine 
wire, so that the small current may 
have the same effect as the large cur- 
rent in the series wound type. The 
resistance of the shunt coils is greater 
than that of the armature, therefore 
variations in the armature will not 
affect materially the magnetizing power 

of the shunt, which will act nearly uniformly as exciter. As 

the current generated by the dynamo increases, the difference 

of potential naturally decreases some, 

because of the resistance of the 

armature and because of the counter 

magnetism. (See §82.) For this 

reason, a field rheostat is generally 

connected in between the two field 

coils, by which the strength of the 

field magnetism can be regulated. 
This dynamo makes both series 

and parallel circuits nearly constant 

as to their working. It is used to 

advantage for stationary machinery. 

III. But multiple circuits require 
of potential, and for this purpose 




Fig. 45. 

a very great constancy 
the compound wound 



ELECTRICAL ENGINEERING 139 

dynamo (See fig. 45) is the best. Each field magnet is wound 
with two separate coils, one of a few turns of thick wire, and 
the other with many turns of fine wire. The thick wire coils 
are in series with the armature and the external circuit, 
and the thin wire coils are, in shunt with the others, con- 
nected with the brushes only. The series winding counter- 
acts the decrease of potential in the shunt. 

In all these different styles, the field windings must be 
connected with the brushes, in order that the proper direction 
may be given to the current generated by the residual mag- 
netism in the field cores. Whenever the direction in which 
the armature rotates, is changed, these connections must be 
reversed. 

For constant current a combination of shunt and separately 
excited winding is preferred, or a combination of a series and 
a magneto machine (armature revolving between poles of 
permanent steel magnet). 

Brushes 

112. Dynamo brushes are generally made of compressed 
graphitic carbon Copper brushes were used formerly for 
dynamos almost exclusively, but were found to be objection- 
able. They consist of copper wire, gauze or strips, soldered 
together at one end; they touch the commutator on a bevel. 
In the case of carbon brushes the surface touching the 
commutator is fitted to its curvature, and touches it either 
radially or on a bevel. Brushes are pressed firmly against 
the commutator by spring holders, which in turn may be 
adjusted in place by a rocker to ensure always area of contact. 

Unless the brushes are in their proper positions, there 
will be considerable sparking, which is destructive to the 
machine and wasteful of electrical energy. When rightly 



140 MODERN ELECTRICITY 

adjusted, two brushes are exactly opposite each other. In a 
dynamo they are placed a trifle in advance of a vertical line 
that might be drawn through the center of the armature in 
figs. 43 — 45, and in a motor a trifle behind this line. 

Brushes should be adjusted before starting the generator, 
unless there is danger of starting it in the wrong direction. 
The current should be turned off before raising the brushes 
from the commutators. Otherwise, in both cases mentioned, 
a spark might arise that would tend to seriously injure the 
commutator. 

Pure carbon is very extensively used as material for brushes. 
A carbon brush well made and properly mounted wears slowly 
and evenly, and it wears lightly on the commutator bars, gliding 
over, rather than gliding against them, without lubrication other 
than that supplied by the graphite of the brush. The bars 
are polished, rather than worn, so that they need not be wiped 
with an oily rag. Very little carbon dust is noticeable on the 
machine, consequently. A carbon brush cannot spread, as a 
copper brush often does, so that the area of contact is constant. 

Armature winding 

113. The manner of winding an armature is of con- 
siderable importance. The position of each single half turn 
of wire should correspond with that of the two adjoining half 
turns, as nearly as possibly. If one half turn from front to 
back (from commutator over to back) passes a north pole, 
then the return half should be laid in such a way that the 
next half turn from front to back may again pass near a 
north pole. Fig. 46 shows, how this is accomplished by lap 
winding, each turn lapping over the preceding one. In the 
diagram, fig. 47, the winding in the ba^j. is the same as in 



ELECTRICAL ENGINEERING 



141 



fig. 46, but in front the two terminals of one full loop do 



a zigzag arrange- 



not run parallel, but diverge, resulting in 
ment. This is called 
wave winding ; it takes 
only about one half 
the number of turns 
required in lap winding, 
produces a better mag- 
netic balance in unpro- 
portional fields, and 
has four times the 
resistance of a lap 
winding. Wave winding permits the use of two brushes for a 
four pole machine, without cross-connecting the commutator. 

Fig. 48 shows a complete armature of modern type. The 
core consists of a number of very thin flat disks of well- 




Fig. 46. 



annealed charcoal iron, the 
being nearly 12 inches, and 



outer diameter of each disk 
its inner diameter 9. Thin 
paper insulates each 
disk from its neigh- 
bors. The armature is 
mounted on a steel 
shaft, to which is 
keyed a non-magnetic 
gunmetal spider with 
four arms, the ends of 
which fit into notches 
cut into the inner edges 
of the core disks. The conductor consists of one layer of 
cotton-covered copper wire of No. 9 standard wire gauge, with 




Fig. 47. 




142 MODERN ELECTRICITY 

a resistance, from brush to brush, of 0*048 ohms. There are, 
in the commutator, 76 bars of hard drawn copper insulated 

from each other by mica 
strips 0-75 mm. in thickness. 
Corresponding to these, there 
are 76 sections, of two convo- 
lutions each, in the armature, 
the adjacent ends of neigh- 
FlG ' 48, boring sections being soldered 

to radial lugs projecting from the commutator bars. The 
armature is bound with turns of fine strong wire in four places, 
to prevent a bulging of the conductors when rotated at high 
speed. 

Calculation of ampere turns 

114. The method of calculating the number of ampere- 
turns required on the field cores was stated in connection 
with the saturation card, in §76. It may be repeated here as 

RULE 34. — To find the number of ampere-turns re- 
quired to drive a given number of lines of force through 
an iron ring, divide the total number of lines of force by 
the ( number of sq. inches of ) cross section of the ring. 
This gives the induction per sq. inch. Then find the cor- 
responding number of ampere-turns per inch in length on the 
saturation curve of the iron; multiply this number by the 
length of the ring in inches. 

When the magnetic circuit is not an iron ring, but 
consists of the parts of a dynamo, the ampere-turns must 
be calculated for each part separately. 



ELECTRICAL ENGINEERING 143 

EXAMPLE 52 . 

How many ampere-turns in the field coils of a bipolar 
dynamo will be required under the following circumstances: 
Lines to be driven through sheet iron armature 1 ,200,000 ; 
armature cross section 12 sq. inches; armature magnetic 
length 8 inches; gap, cross section, 10 sq. inches, gap 
length 2 X * 1 1 = '22 inches ; leakage coefficient 0*9 ; cast 
steel field poles, cross section, 16 sq. inches ; magnetic length 
40 inches; cast steel yoke, cross section, 24 sq. inches; 
magnetic length 12 inches? 

Armature induction, 1,200,000-5- 12= 100,000 per sq. in. 
Therefore ampere-turns per inch, by saturation curve : 60. 
8 X 60 = 480. 

Gap induction, 1,200,000-5-10 = 120,000; 120.000X -3133 
= 37-596 ampere-turns per inch of length. 37*596 X *22 = 
8,271. 

Pole induction, 1,200,000-5-0-9 = 1,333,333; 1,333,333 
*- 16 = 83,333 per sq. inch, which, as the saturation curve 
indicates, require 90 ampere-turns per inch. 90 X 40 = 3600. 

Yoke induction, 1,200,000 -*- 24 = 50,000 per sq. inch, 
which as the saturation curve indicates, require 55 ampere- 
turns per inch. 12 X 55 = 660. 

A 80 + 8 ,27 1 + 3600 + 660 = 1 30 1 1 . 13 ,000 ampere-turns 
for the field coils. Ans 



RULE 35. — The number of ampere-turns required per 
ceil on a multipolar armature having one coil per pole, 
equals the sum of the ampere-turns required to drive the 
lines of force through the armature, one gap, one pole and 
the yoke as far as half the distance to the next pole. (See 
§ 76.) The result must be multiplied by two, if there is 
only one coil to two poles. 



144 MODERN ELECTRICITY 

EXAMPLE 53. 
How many ampere-turns per coil will be required in an 
iron clad multipolar dynamo ( see § 108), under the follow- 
ing circumstances : 

Lines to be driven from one pole through the sheet iron 
teeth, 6,000,000 ; cross section of teeth of armature under one 
pole, 60 sq. inches; magnetic length of teeth 1*25 inches; 
cross section of armature core, 70*5 sq. inches; armature 
core magnetic length, 7 inches; gap cross section, 121 sq. 
inches; gap magnetic length, 0-1 inch; leakage coefficient 
0*9 ; cast iron field pole cross section, 90 sq. inches ; mag- 
netic length of field pole, 15 inches; cast iron yoke cross 
section, 81 sq. inches; yoke length 12 inches? 

Armature teeth induction, 6,000,000-^60=100,000 per 
sq. inch. Therefore ampere-turns per inch, by saturation 
curve, 60; 1-25X60 = 75. 

Armature core induction, 3,000,000 -s- 70*5= 42,555 per 
sq. inch. Therefore ampere-turns per inch, by saturation 
curve, 36; 36X7=252. 

Gap induction, 6,000,000^- 121 =49,669 ; 49,669 X -3133 
= 15,561 ampere-turns per inch of length, 15,561 X0*1 = 
1556. 

Pole induction, 6,000,000-^0-9 = 6,666,666; 6,666,666-^- 
90 = 740,740 per sq. inch, requiring, by the saturation curve, 
500 ampere-turns per inch; 1 5 X 500 = 7500. 

Yoke induction, 3,333,333 -*- 81 = 41,152 per sq. inch, 
requiring, by the saturation curve, 40 ampere-turns per inch; 
12X40 = 480. 

75+252 +1556 + 7500 + 48 = 9431 ampere-turns for 
each field coil. Ans. 

Efficiency of a motor ; torque 

115. The magnetism set up by the current in the coils of 
a revolving generator armature, interferes with the magnetic 
lines of force of the field, the effect of which tends to stop 



ELECTRICAL ENGINEERING 



145 



the motion. This counter force cannot be avoided ; it must be 
overcome by bringing to bear a certain extra amount of power 
sufficient to keep the armature moving. The torque of a 
dynamo which the engine produces must be equal to the torque 
reaction of the load on the dynamo. From a mechanical 
standpoint it is measured in foot pounds, which is equal to the 
force applied times its arm. For instance an engine is belted to 
a generator. Assume that it applies a force of 8,000 lbs. at the 
rim of a 24-inch pulley on the generator. The torque is equal 
8,000X1 (which is the radius of the pulley)=8,000 ft. pounds. 
Likewise or rather reversely, in a motor 
the magnetic field sets up a counter 




Fig. 49. — Electrical Hoisting Machine. 

Direct current motor of 16 H. P. 1455 revolutions per minute. 550 volts. 
Raises 11,000 pounds W% inches per second. 

electric pressure in the revolving armature, which tends to 
stop the motion, and consequently an extra amount of current 
must be supplied to the armature to keep it moving. If the 
counter E. M. F. in a motor is so strong that the motor cannot 
do its work, a slackening of its speed, or a weakening of the 
field, will mend matters, as by either of these means the 
counter E. M. F. will grow less. 



146 MODERN ELECTRICITY 

This amount of extra power must be added to other losses 

already mentioned, as hysteresis, the I 2 R loss, eddy currents, 

and the friction converted into heat ; and the aggregate of all 

these must be subtracted from the "input" power, to arrive at 

the efficiency of a machine, which is generally expressed by 

the ratio: output divided by input. 

,,. . Power input — losses 

Hence, efficiency = : 

Power input 

EXAMPLE 54. 
A motor which at full load supplies 30 horse power and 
requires 50 kilowatts, has a full load efficiency of about 45 
per cent. (30 X 746 -f- 50,000 = 0-4476.) 

EXAMPLE 55. 

A dynamo which has an efficiency of 90 per cent and 
requires 30 H. P. at full load, supplies 24-8 kilowatts. 
(30X746-0-9 = 24,866.) 

Questions and Answers. 

Q. What is the Board of Trade unit ? 

A. It is the amount of electrical energy of a current of 
1000 amperes at a pressure of one volt during one hour. 
By this unit ( kilowatt-hour ) electricity is measured and 
sold. 

Q. Does the going astray of lines of force on their way 
between the pole pieces of a dynamo cause a loss of power? 

A. Not exactly. 

Q. To what is it due? 

A. It is due to a disproportion between pole pieces and 
armature core, in size or shape. 

Q. What is meant by "uvercompounded " ? 



ELECTRICAL ENGINEERING 147 

A. If the effect of the series coils is made to preponde- 
rate over the shunt coils, resulting in a higher potential 
difference at the brushes, the machine is said to be over- 
compounded. 

Q. What kind of winding is used on the fields of a street 
car motor, and why ? 

A. A series winding; because its torque in starting is 
great, and because it increases with increasing current. 

Q. Of what kind of iron is the magnetic circuit in a machine 
made ? 

A. Where a great weight is not objectionable, cast iron 
is used. Wrought iron has a greater permeability and is 
therefore preferred because it allows of lesser weight, but it 
is more expensive. Where very light weight is desirable, 
soft cast steel is used, as in railway motors. 

Q. How are armature cores fastened to the shaft? 

A. The thin disks of iron or steel are fastened by means 
of clamps and keys. 

Q. What is the advantage of having iron^clad motors in 
a street car? 

A. The frame surrounding the armature protects it from 
dirt and especially from water, which would destroy the 
insulation of the armature wire very rapidly. 

Q. How are the poles of multipolar machines wound? 
A. The same as in bipolar machines. 
Q. What is done, if the position of "no sparking" changes 
with the load on the machine ? 

A. As the load increases, ' the brushes must be moved 
forward on a dynamo, and backward on a motor. This is 
generally done automatically. 



148 MODERN ELECTRICITY 

Q. What is meant by "load" on a machine ? 

A. It means the amount of current required by an electric 
circuit during a given time. When all the cars of an 
electric street railway are running, the load is heavy ; when 
most of them happen to stop at street corners along the 
route at the same time, the load is light. 

Q. What is the leakage coefficient ? 

A. The ratio of lines of force going through the field, to 
those going through the armature ; In other words, the ratio of 
total amount of magnetic lines of force to the amount of 
"useful" magnetic lines of force. 

Q. What does it mean, when it is stated that the leakage 
coefficient of a machine is 1 '05 ? 

A. It means that the ratio of the total of the magnetic 
lines of force to the "useful" magnetic lines of force is 1*05. 

Q. What advantages has a drum armature over a ring 
armature ? 

A. First, the drum armature offers less magnetic resis- 
tance, because a given magneto-motive force can urge 
more lines of force through its larger mass of iron. Second, 
all the lines passing the drum armature are usefully cut 
by the conductors, and for this reason a slow speed will 
set up an E. M. F. equal to that of a ring armature at 
higher speed. Third, having very little idle wire, the resis- 
tance is lower. 

Q. What disadvantages has it? 

A. It cannot be made as strong mechanically as the ring 
armature, and the cross connections are apt to give trouble. 







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CHAPTER IX. — Alternate Current Machines. 



Alternate Currents 

116. A simple coil when revolving in a magnetic field so 
as to cut magnetic lines of force, sets up an electromotive 
force, which changes direction, according to the position of 
the coil, at every half turn. (See § 81.) The currents thus 
produced are called alternate currents, in contrast to the 
direct or continuous current received at the brushes of a 
direct current dynamo. In each half revolution of the ring 
in the magnetic field an electromotive force is generated 
which rises from naught to a maximum, and then falls again 
from the maximum to naught. The complete changes dur- 
ing one whole revolution constitute one period, and the total 
number of periods produced in one second is called the 
frequency. The frequency of a two-pole machine equals the 
number of revolutions per second. In any other machine, if 



p = number of poles, n=x. p. m., /= frequency, then/ 



p n 



Hydraulic Analogy 

117. A continuous current of electri- 
city may be compared to the flow set 
up by a centrifugal pump, while a pul- 
sating current resembles the flow from a 
common piston pump. The flow of 
alternate currents may be compared to 
the flow of water in the apparatus shown 
in fig. 50. A and B are glass cylinders 
of equal diameter, the bottoms of which are connected 
by means of a pipe C, which is of smaller diameter 

149 




Fig. 50. 



150 



MODERN ELECTRICITY 



than the cylinders. The pistons D and E are connected 
by means of an arm F which is so pivoted that, when 
piston E is pressed down, piston D is forced up, and 
the water contained in cylinder B flows through the con- 
necting pipe C into the cylinder A. When piston D is 
pressed down, piston E is forced up, and the current flows 
from cylinder A to B, in the opposite direction of the former 
current. When the pistons are rapidly moved up and down, 
an alternate current is produced in pipe C. 

When each piston is moved up and down once in a second, 
then the period of their complete action is one second and 
the frequency is one period per second, 

Pressure curve of alternate currents; Sine curve 

118. Imagine that A in fig. 51 is the cross section of a 
wire of a simple coil revolving, in the direction of the arrow, 

■L 




Fig. 51, 



around the axis in the magnetic field between the magnet 
poles N (north) and 5 (south). At the instant when this 
wire is in position A or B, there is no current in the wire, 
because it moves, in that instant, almost parallel with the 
magnetic lines of force extending from TV to 5. At these 
points the pressure is said to be minimum (=0). When 



ELECTRICAL ENGINEERING 151 

in position C or D, the maximum pressure is in the con- 
ductor, because it cuts the magnetic lines of force at right 
angles. 

The pressure curve of this conductor may be constructed 
as follows : For convenience, assume the highest pressure, 
at points C and D, to equal one, and also take the radius 
(CO = OD = ^- diameter CD) of the revolving conductor 
to equal one. (As one inch.) On the prolonged line A B 
measure off the line of travel described by the conductor 
A in one revolution from A, through C, B, D, back to A. 
As the diameter of the circle equals 2, the path of conductor 
A equals 77 X diameter = 3- 1416 X 2 = 62832, or about 
6*3 times the radius (CO), taken as unit. Mark the ends 
of line thus obtained A' and A". The position of A when 
it starts to revolve, is represented by the point A'; its path 
from A to C equals \ of the circumference of the circle, 
or, in the diagram, \ of the line A' A". (A'C = \ A' A".) 

The wire's route from A to B equals ^ of the circum- 
ference of the circle, or, in the diagram, £ of the line A'A" 
(A , B , = B , A M ),andso on. Then A'C = C'B'= B'D' = D'A" 
_ A'A" 
4 * 

In points C and D the pressure equals one, or, graphi- 
cally, the length of radius CO. This pressure may be repre- 
sented in the diagram by perpendicular lines of the length 
of CO in points C and D'. Then C'C" = D'D"~ = CO 
= 1. Since the flow of the current during the ^ revolu- 
tion from B to A is opposite to that of the current in the 
first half revolution, from A to B, the perpendicular D'D" 
must be measured off in the opposite direction from C'C" 



152 MODERN ELECTRICITY 

Pressure in the conductor A, when in position A or B, 
is = 0, and is therefore represented in the diagram by 
points A', B\ A" respectively. 

The pressure curve of the current must therefore pass 
through A', C", B\ D", A". For the precise construction of 
the pressure curve, other points through which it must pass 
may be found as follows : Divide the quadrant AC in four 
equal parts by points a, b, c. These 4 parts may be repre- 
sented in the diagram by lengths A'a' = a'b' = bV = c'C 
= \ A'C\ The pressure in the conductor when at points 
a, b, c, therefore, equals the lengths of the normals falling 
from these points on the diameter A B : ad, be, ef 
respectively. Now draw perpendiculars in points a', b\ c' 
in the diagram, and make . a'a" = ad, b'b" = be, c'c" =cf, 
in the same direction as C'C". In the same manner points 
of the pressure curve above the line between C" and B', 
and below the line, between B' and D", and D" and A" 
may be found. By connecting the points thus obtained, the 
pressure curve of one period or cycle is established. 

The result of this construction is a smooth curve ; in 
practice the actual curves of pressure of alternate current 
dynamos are irregular, owing to various conditions affecting 
current. The curve A'C" B' D" A" is termed the sine curve. 

Electromagnetic Inertia; Self=induction 

119. Whenever the strength of a current in a conductor 
increases or decreases, another current is induced, in the 
same circuit or in a neighboring one, by means of changes 
in the magnetic field surrounding the conductor. If these 
magnetic lines of force cut some parts of the circuit, the 
current of which induced them, they act inductively on 




153 



154 MODERN ELECTRICITY 

this current. In § 83 it has been also mentioned that a 
coil possessing many turns, has a great self-induction, which 
will be all the greater if the coil contains an iron core. 

A coil which generates a certain number of magnetic 
lines of force when a certain current is turned on to pass 
through its turns, will also generate a current, when a magnet 
pole having the same number of magnetic lines of force, as 
were generated in the coil, is plunged into the coil. And 
the drawing of this magnet from the coil will act in the 
same manner upon the turns of the coil, as the cutting off 
of the current of the coil would act on the magnetic lines 
of force within the coil. The current which is induced when 
the magnet is plunged into the coil, tends to push the mag- 
net pole out of the coil, while the current induced by with- 
drawing the pole tends to keep the magnet in the coil. It 
is evident that in both cases the self-induced E. M. F. 
opposes any change ; when the current is turned on, it tends 
to hinder the growing of the current; when the current is 
turned off, it tends to keep the current flowing. This tend- 
ency of self-induced electromotive force to oppose any change 
is called electromagnetic inertia. // is due to the magnetic 
effect of the current, and, in its turn, it causes self- 
induction. 

All bodies have an inertia of their own, that opposes any 
change. Every body resists being moved from place to 
place, being bent, crushed, heated, or being stopped when in 
motion. 

Angle of lag 

120. Those familiar with the seashore know that the tide 
does not rise to the same height, and the ebb does not fall 



ELECTRICAL ENGINEERING 155 

to the same level, in all channels. In a straight, deep and 
smooth channel, A, the flow is swifter than in a tortuous, 
shallow and rough one, B, and the result is, that the differ- 
ence between the highest tide and the lowest ebb at a point 
remote from the open sea, is much larger in A than in B. 
The flow in B may be said to be, or lag in phase, behind the 
flow in A. Similarly, the alternating current generated in a 
dynamo never keeps step with the alternating electromotive 
force. The self-induction within the circuit (See §119) 
causes the cur- 
rent to lag in 
phase behind its 
electromotive 
force by a small 
fraction of a sec- 

, D , co , Fig. 52. 

ond. Fig. 52 is a 

diagram of a current lagging in phase behind the electromo- 
tive force. The lagging current is shown in heavy line, the 
leading voltage in thin line. But self-induction does not only 
cause a lagging of the current ; it also chokes the current 
down, the increasing current being opposed by the increasing 
self-induction. 

The amount of lag is expressed in terms of degrees. In 
fig. 51 the line A' A" maybe considered to be divided into 
360 parts, like the circumference of the circle A C B D. 
Then, if the wave line A' C" B' D" A" represents the wave 
of the B. M. F., and a si miliar current wave passes through 
C and D', the current wave would be half way behind the 
E. M. F. wave, and the angle of lag would be 90°. As 
some power is required to send a current through a circuit 




156 MODERN ELECTRICITY 

of even the slightest resistance, it is impossible to have a 
lag of quite 90°. 

Co=efficient of self-induction ; Impedance 

121. Inductance is that property, in virtue of which a 
given electromotive force acting on a circuit does not imme- 
diately generate the full current due to its resistance; and 
when the electromotive force is withdrawn, time is required 
for the current strength to fall to zero. 

The number of the lines of force which, springing out 
from and collapsing upon the various convolutions of a coil, 
cut the other convolutions, depends upon the current strength, 
but also upon the shape of the coil, that is, upon the number 
of convolutions in the coil and their disposition. This latter 
factor is termed the co-efficient of self-induction of the 
coil, and it may be measured in terms of a unit called the 
henry. If a current is started in a coil, the inductance 
generates a counter E. M. F. proportional at any instant to 
the rate at which the current is changing in strength ; and 
if the current rises uniformly during one second from zero 
to one ampere, and if the counter E. M. F. during that 
second is one volt, then the coefficient of self-induction of 
the coil is one henry. It is generally denoted by the symbol 
L, and it is constant in value for a coil without iron. 

The total number of lines of force interlinked in the coils 
varies with the current strength, and is equal to the product 
of L and I. The total inductance is equal to L times the 
rate at which the current is changing in strength. It is 
evident that with an alternating current the inductance will 
increase as the maximum value of the current is increased. 

If the coil has an iron core, the value of L is enormously 



ELECTRICAL ENGINEERING 157 

increased, but is no longer constant, varying according to the 
permeability curve of the iron. 

To set up a direct current of 60 amperes through a 
resistance of 3 ohms, an E. M. F. of 180 volts is necessary. 
In an alternate current circuit this voltage would not suffice 
to generate the required 60 amperes, in case there is 
self-induction in the circuit. By the aid of geometrical con- 
struction the formula for the alternate current has been found 
to be : 

/= or in words 



v 



R 2 +4tt2/ 2 u 



RULE 36. — The alternating current of a circuit equals 
the E. M. F. (E) divided by the square root of the sum of the 
square of resistance (R), and four times the product of the 
squares of ir, number of periods per second ( f ) and coefficient 
of self-induction (L). (See footnote, p. 61). 

From this formula the necessary voltage may be found : 



E = /xJ R2 + 47r2 f 2 L2 or in words: 

RULE 37. — The E. M. F. in an alternate current circuit 
equals the current multiplied by the square root of the sum of 
square of resistance and four times the product of squares of 
tt, number of periods per second and coefficient of self-induction. 



The expression JR 2 + 4 7r 2 / 2 L 2 is usually called the 

impedance (z). The impedance is the ohmic resistance of the 
circuit, plus the effect of self-induction, which depends upon 



158 MODERN ELECTRICITY 

the magnetic effects in the circuit, and upon the frequency 
of the current. 

If R is of negligible value, the above formulas become : 



E 



I 4 tt2/ 2 ^ 2 = 2 irf L I 



E 
and L = 7-7 or in words 

2 7T / / 



RULE 38. — E. M. F. equals two times tt , times the 
number of periods per second, times inductance times current, 
and 

RULE 39. — Inductance of a circuit equals E. M. F. 
divided by twice it, times number of periods per second times 
current. 

EXAMPLE 56. 

What is the coefficient of self-induction in a coil of 
negligible resistance, through which a current of 50 amperes 
and a frequency of 200 periods per second is sent at a 
Dressure of 15,708 volts? 



5708 15708 1 



= 7 . Ans 



2irfl 2 X 3-1416X200X50 "62832 4 

EXAMPLE 57. 

What pressure is required to send a current of 4 amperes 
and a frequency of 250 periods per second through a coil 
of negligible resistance, whose coefficent of inductance is 
075? 

E=2tt f L 7=2X3-1416X 250X075X 4 = 
6283-2X075 = 4 7/2-4 wits. Ans. 



ELECTRICAL ENGINEERING 159 

EXAMPLE 58. 

Zr= 20,000 volts, number of periods per second 796, 

self-induction 10, resistance negligible, (05 ohm). What 

is the current ? 

B 20,000 n . A 

/ = — — -,—■ — =04 amp. Ans. 

2* j L 5005X 10 

Choking Coils 

122. It is evident that, when there is in a circuit a low 

ohmic resistance and a great effect of self-induction, the 
current will be governed by the self-induction. Coils of 
small resistance and large self-induction are used to impede 
alternate currents. They are called impedance coils or choking 
coils. The greater the coefficient of seif-induction is, the 
lower will the actual valu^ of the current fall below the 
value it would have, if no self-induction existed. See §120 

Chemical Effect of Alternate Current 

123. When the poles of an alternate current dynamo are 
connected to an electrolytic cell, no metal is carried by the 
current from anode to cathode. An alternate current las 
no electrolytic effect, because of the rapid changes in the 
direction of flow, making one plate of the cell alternately 
for one instant an anode, and for the next instant a 
cathode* The particles detached from the plate when anode 
are driven back to it when cathode. 

Effective current; effective pressure 

124. The heat produced by a continuous current ( see 

§60). equals the current squared times the resistance of 
the circuit. In alternating currents V e heating effect changes 
with the current at every instant, but the sum of all the 



160 MODERN ELECTRICITY 

instantaneous values is greater than that of a continuous current 
equal to its average value. The effective value of an alternat- 
ing current is numerically equal to a steady direct current 
which will produce the same heating effect in a given time as 
will a changing alternating current. Effective value = 707 
maximum value = I'll average value. 

The reason for this is that the differences and averages in a 
progression of squares are larger than those in the progression 
of their roots. The differences between 3, 6, 9, for instance, 
are 3 and 3, while the average of the three numbers is 6. But 
the differences between the squares of these figures, 9, 36,81, 
are 27 and 45, and their average is 42. For the same reason, 
the heating effect of a pulsating current is greater than that of 
a continuous current equal in its average value, which in turn, 
= *636 maximum value. 

The current and pressure set up without self-induction or 
other disturbing elements, are called effective current and 

EFFECTIVE PRESSURE. 

The value of an alternating current squared, times the 
resistance of the circuit, gives the heating effect of the 
current. The value is called the effective current. 

The effective pressure of an alternating current is the value 
which, when multiplied by the effective current set up by it in 
the circuit, gives the power expended in the circuit. 

RULE 40. — The effective current (or effective pressure) 
of an alternating current equals the square root of the average 
of all the squares of the instantaneous values of the current {or 
pressure) during one half period. 

Measuring alternate currents 

125. The watts expended by an alternate current dynamo 
cannot be measured in the same way as the power of a direct 
current generator, employing the voltmeter and the ampereme- 
ter separately, and multiplying the results obtained by these two 
instruments. Owing to the difference of phase, which does not 



ELECTRICAL ENGINEERING 161 

interfere with the workings of these instruments, the results 
thus obtained would greatly differ from the true watts which 
the dynamo expends. 

Therefore, in measuring the power of alternate currents a 
wattmeter is used (usually an electrodynamometer, see § 90), 
with a high resistanse coil for connecting across the terminals, 
and a low resistance coil for connecting in series with the cir- 
cuit. However, if the E. M. F. and the current are in phase the 
watts are equal to the product of the two. If they are not in 
phase the angular difference must be taken into account. The 
power is P= EI cos cj>. Cos cf> is called the power factor. 
The power factor times the E. M. F. times the current equals 
the true power. 

EXAMPLE 59. 

An alternate current makes 9000 alternations in five 
minutes. What is its frequency ? 

9000 9000 . , J A 

2X5X60 = ^00 = ] 5 pen ° dS p6r SeCOnd ' AnS - 

EXAMPLE 60. 
An alternating current has a frequency of 150 periods per 
second. How many alternations does it make in one hour? 
1 50 X 2 X 60 X 60 = 300 X 3600 = 1 ,080,000. Ans. 

EXAMPLE 61. 

What is the coefficient of self-induction of a coil whose 

resistance is negligible, through which flows a current of 100 

amperes and a frequency of 100 periods per seconds at a 

pressure of 15 708 volts? 

15708 15708 _ A 
. = = 0-2S An<5 

2X3-1416X100X100 62832 

EXAMPLE 62. 
What pressure is required to send a current of 100 am- 
peres and a frequency of 200 periods per second through 



162 MODERN ELECTRICITY 

a coil of negligible resistance and of a coefficient of self- 
induction, 02 ? 

2X3-1416X200X0-2X 100 = 
1 256-64 X 20 = 25 , 1 32 volts. Ans. 

EXAMPLE 63. 
What are the periods in the above four examples ? 

L 4 2: >ik 3 -)4 4 -W Ans - 

Alternate currents of high frequency 

126. Formerly currents of a frequency of not more than 
100 to 150 periods per second were employed; nowadays 
currents of 1000 and more periods per second are in practi- 
cal use. For electric lighting the frequency varies from 60 
to 120 periods per second. In cases, where a frequency of 
1000 and more periods per second is used, the current does 
not seem to flow through the whole cross section of the 
wire, but rather to be confined to its outer surface, as the 
conductor offers a great impedance to it. And this fact lends 
a certain strength to the most modern supposition of scien- 
tists, that after all "electrical energy is not transmitted through 
the wire itself, but through a medium surrounding the wire/' 

Alternate current in electromagnets 

127. If an alternate current is sent through the coil of an 
electromagnet, an alternating magnetic field will be produced, 
and the core of the electromagnet will be alternately mag- 
netized north and south. Electromagnets to be supplied 
with alternate currents are usually designed with fewer 
turns than those which are supplied with direct current. 




x6 3 _. 



164 



MODERN ELECTRICITY 



Their cores are laminated, in the same manner as the 
drums of direct current dynamos (see §102), to avoid eddy 
currents which are set up by the alternate current, to such 
an extent, that even electromagnets with laminated cores 
repel particles of copper. 

Transformers 

128. For the sake of economizing copper in feeders for 
long distances, the current is transmitted through them 
at a high pressure, permitting a smaller section of wire. 
But arriving at the point of distribution, where the current 
is to be utilized, say for lighting incandescent lamps, the 
high pressure current (of 5000 or 10,000 volts and higher) must 
be transformed to one of low pressure (of say 110 volts). 
Apparatus designed for this purpose are called transformers. 
They are modified induction coils, (see § 82 and 83), with well 

laminated cores composed of 
thin soft sheet-iron of such a 
shape that the magnetic circuit 
is closed. Upon this core (C in 
fig. 53) there are two coils : the 

C' :: %, C""'Sj:;: ;: . ) primary (A) which receives the 
' <^ alternate current, and the sec- 
*/ ondary (B) which gives out the 
FlG# ^ transformed current. The pri- 

mary consists of many turns of fine, well insulated copper 
wire to receive a small current at high pressure ; the second- 
ary consists of a few turns of thick wire, to give out a large 
current of low pressure. 

If the primary coil has 2500 turns, and the secondary 50 
turns, then the ratio of their windings is 2500^-50 = 50-^- 1, 




ELECTRICAL ENGINEERING 165 

and if the secondary coil is to furnish 200 amperes at 50 
volts, then the primary coil must supply at least 4 amperes 
(200^-50) at 2500 volts (50X50). 

On the other hand, in a transformer which is to transform 
5000 volts down to 100 volts, the ratio of the primary and 

5000 
secondary windings must necessarily be = 50-^ 1 .which 

means that for every 50 windings of thin wire on the primary 
coil 1 winding of thick wire on the secondary coil is required. 
The current, without regard to the pressure, is in the inverse 
ratio, as the power (in watts) put into the transformer equals 
the power taken out of it. 

There is only small loss in transformation. The iron loss 
(caused by eddy currents and hysteresis of the core,) and 
the copper loss, (due to the ohmic resistance of the copper 
wire), either of -these amounting to about 0-8 to 1 per cent 
of the supplied power, are negligible quantities. It is 
important to keep these losses low, because the secondary 
coil of a transformer is generally on open circuit during the 
greater part of the time. 

If the rate of alternation is 100 per second, the E.M.F. 
will be applied to the primary coil in one direction during 

— ■ th part of a second, and during the greater part of this 

ZUv 

small period it is far below its maximum value, the angle 
of lag being nearly 90°; the reversal takes place long before 
the current has had time to rise to any appreciable strength. 
This fact, and the high self-induction of the primary coil are 
the causes of the smallness of its current 



156 MODERN ELECTRICITY 

Automatic self=regulation 

129. When the secondary circuit is closed, the alternating 
potential difference at the terminals of the secondary coil 
sets up a current, which is inversely proportional to the resis- 
tance of the external secondary circuit, if the resistance of 
the secondary coil is negligibly small. 

This secondary current has a reactive effect enabling the 
primary coil to take up more power from the mains, first 
by increasing the primary current, and second by reducing 
the angle of lag between the E. M. F. and current. In a 
perfect transformer this power would be inversely propor- 
tional to the resistance of the secondary circuit. (See § 
82.) When the current starts in the secondary coil, its lines 
of force, in springing out to pass the iron core, must cut 
the primary coil convolutions, and the E. M. F. thus 
generated is in such a direction as to assist the primary 
E. M. F. in increasing the primary current, while the collaps- 
ing secondary lines of force assist the reversal of the primary 
current. This reaction is greatest when most needed, making 
the transformer self-regulating. The eddy currents in the 
iron core have the same reacting effect on the primary 
current. 

This self-regulation of the transformer is assisted by 
several devices. In the Thomson sliding-coil transformer 
one winding is movably mounted, and any increase in the 
secondary current, due to short-circuiting some of the 
devices, or to a similar cause, will produce an increased 
repulsion between the two windings, driving them farther 
apart. When sufficiently far apart to reduce the mutual 
induction enough to bring the secondary current back to 



ELECTRICAL ENGINEERING 



167 



normal strength, a state of equilibrium sets in again, and 
the windings resume their proper distance. In other types 
of transformers, the axis of one winding is pivoted, so that 
it may turn out of and into parallelism with the axis of 
the other winding, with the same results as above described. 

Location of transformers 

130. A transformer is usually well insulated and enclosed 
in a cast iron box which keeps it free from moisture. 
The high pressure currents are carried either from the 
central station to special sub-stations, (or transformer sta- 
tions,) from where low pressure mains distribute the current 
to the houses, or the high pressure current enters each 
building in high pressure mains, and is transformed in the 
building by means of a transformer placed in the cellar. Such 
distributing systems are shown in figs. 54 and 55. Trans- 
formers are also placed on the poles carrying the wires. 

HIGH PRESSURE MAINS mGH pRE$suRE MA|N5 




Fig. 54. 



Fig. 55. 



EXAMPLE 64. 
The primary coil of a transformer has 1000 turns, the 
secondary 100 turns. What is the ratio of their windings? 
1000 

Too = 10, 10: l Ans ' 



168 MODERN ELECTRICITY 

EXAMPLE 65. 

A transformer of 4000 turns in the primary coil gives 
the secondary winding a pressure of 250 volts. How many 
turns has the secondary winding, when the primary pressure 
is 1000 volts? 

1000 . * . j. 

-— — = 4 ; ratio of windings is 4:1. 

4000 ^-4= 1000, The secondary winding has 1 ,000 turns. 
Ans. 

EXAMPLE 66. 

The primary coil of a transformer is supplied with a 
current of 2000 volts at 25 amperes. The pressure received 
from the secondary is 250 volts. What is the current from 
the secondary coil, if the iron and copper losses are of 
negligible value ? 

Input — output. 2000 X 25 = 50,000 watts. Watts -s- volts 
= amperes. 50,000-^-250 = 200 amperes. Ans. 

EXAMPLE 67. 

The primary coil of a transformer whose ratio of windings 

is 20-^-1 receives 15 kilowatts at 2000 volts. What is 

the output of this transformer in volts and amperes, when 

the losses are of negligible value ? 

15000 „ ^ . 

In the primary = 7-5 amperes; in the secondary 

K J 2 000 

2000 1 5000 

— — = 100 volts, and — - — — = 150 amperes. Ans. 
20 100 y 

Transformers designed for the purpose of reducing high- 
voltage currents into low-voltage currents are commonly 
called step-down transformers. Sometimes transformers are 
used to raise the pressure in order to economically transmit 
energy over long distances, and this kind of transformers 
is called step-up transformers. 



ELECTRICAL ENGINEERING 169 

The booster 

131. Of late the system of having a large number of 
small insulated transformers delivering currents at about 
50 volts, has been superseded in many cases by installing 
large transformers in sub stations, and by the use of 100 
to 500 volts on the secondary side. This renders possible 
a considerable increase in secondary output, but, of course, 
it also necessitates a corresponding increase in the length 
of secondary feeders, and these feeders must be large enough 
to avoid an excessive drop, even though the maximum load 
may be on for a very small portion of the time only. In 
such a case the use of a booster (subsidiary generator) 
is very economical, as by its aid the size of wire may be 
reduced considerably. For instance, there are three main 
generators, over-compounded so as to give a pressure of 500 
volts at no load and 550 volts at full load. The dynamos 
being joined in parallel to the bus bars, would suffice for an 
increase in the total load, but not for a heavy increase in 
any one feeder circuit. In such an event a booster set is 
employed, consisting of a 20 volt series wound dynamo, 
joined directly in the feeder circuit, and driven at a constant 
speed by a shunt motor connected directly across the mains. 

Alternators 

132. Alternate current generators or alternators are con- 
structed upon the same principles as direct current dynamos, 
but are readily distinguished from them by the fact that they 
possess collecting rings in place of the commutator. In practice 
alternators are used which generate currents of 1000 to 5000 
volts pressure, with frequencies of 25 to 120 periods per 
second, because of the economy «n copper when transmitting 



170 MODERN ELECTRICITY 

power over long distances. Therefore almost all alternators 
are designed as multipolar generators, with stationary arma- 
ture and rotating field magnets, Alternators possess the 
advantage over direct current generators, that they do away 
with the commutator and with the great difficulties connected 
with its use. 

Armatures are mostly wound in coils connected together 
in series, the ends of the first and last coil being connected 
to the two separate collecting rings or slip-rings. (See fig. 61 , 
§ 136.) The number of poles of the field magnet equals 
usually the number of coils on the armature. 

RULE 41 . — The number of alternations in a certain time 
equals the number of polepieces in the field magnet times the 
number of revolutions of the armature in that time. 

Types of alternators 

133. There are various types of alternators, the most 
important of which are the following: 

1. Alternators v/hose armature is stationary, and whose field 
magnet revolves. From this kind of alternators the current 
is taken from the stationary armature by means of connect- 
ing posts (Ferranti, and Mordey types.) 

2. Alternators, whose field magnet is stationary and whose 
armature revolves. From these machines the current is 
taken by means of brushes rubbing against two or more col- 
lecting rings. (Siemens and Schuckert types.) 

3. Alternators, whose field magnet and armature are both 
stationary. The current is induced by means of revolving 
iron keepers or inductors which induce currents in the sta- 
tionary armature by making and breaking the magnetic circuit 



ELECTRICAL ENGINEERING 



171 



of the field magnets. From these machines the current is 
taken as under 1. 

The rotating keepers, laminated masses of iron, carried on 
a circular non-magnetic framework, effect the cutting of the 
armature conductor by the lines of force set up by the field 
magnet, in such a manner that first a very good and then 
a very bad magnetic circuit are alternately set up. A typical 
inductor alternator may be described here . 

The stationary outer iron ring has inwardly projecting pole- 
pieces which are wound alternately with field magnet and 
armature coils. The 



field magnets alter- 
nate in polarity. (In 
the diagram, fig. 56, 
the armature cores 
are marked A, the 
pole-pieces are 
marked TV and 5, and 
the arrows indicate 
the direction of the exciting current. The keepers are lettered 
K.) In the position shown in the diagram, the maximum 
number of lines pass from the adjacent magnet pole through 
each armature coil, and the E. M. F. is zero, the reversal 
in the direction of the current taking place at this moment. 
As each mass K moves onward, the air gap increases, and 
the number of lines of force from, say, an S pole, threading 
an armature coil, is lessened, while lines of force from 
the next TV pole are beginning to thread through the armature 
in the opposite direction. When the middle of each keeper 
is directly opposite the middle of an armature coil, two 




Fi g. 56. 



172 



MODERN ELECTRICITY 



sets of lines of force, equal in number, opposite in direction, 
pass through the armature coil, and the E. M. F. is at its 
maximum. 

The keepers are rotated at the speed necessary to produce 
the desired rate of alternation or periodicity. If the revolving 
part is truly balanced, this speed involves no mechanical 
difficulty, such as arise in rotating the complicated mass 
of iron, copper wire and insulating material in an armature. 

Field excitation of alternators 

134. As the current generated by alternators cannot be 
used to excite the field magnet, another, direct current is 
employed for this purpose. This current is usually generated 
by a small separate direct current dynamo — the Exciter. A 
rheostat connected in the field of the exciter or of the 
alternator, or both, regulates the pressure. 

Regulation may also be done by having a rectifying com- 
mutator near the collect- 
ing rings, which allows a 
small direct current to 
pass through a few turns of 
wire on the field magnets 
This composite excitation 
may be compared to the 
compound winding of 
direct current machines. 
Field magnets of alternators 

i35« Some kinds of field magnets of alternators differ from 
the field magnets of direct current generators. A special 
form of field magnets, known as Elwell-Parker type, is shown 
in fig. 57. The magnetic poles are marked N and 5. 




ELECTRICAL ENGINEERING 



173 




Fig. 58. 



The Siemens alternating current dynamo (see fig. 58) has 
two opposing crowns of cylindrical electro-magnets, the face 
pole-pieces being of opposite 
polarity. The armature coils 
in fig. 58 are only indicated. 
The lines of force pass from 
pole to pole, straight across 
the armature space. The ar- 
mature coils, in revolving, cut 
through a series of powerful 
fields, with the lines of force 
alternating in directions. The 
armature coils equal the fields in number, therefore they are 
equally active at any given moment. In the position shown in 
fig. 58 the coils are just opposite the bobbins, and the two 
halves of each coil are cutting lines of force all due to one pair 
of opposite magnets, and, therefore, ali in one direction. The 
two E. M. F.'s induced in the two halves of the coil neutralize 
each other. At this moment the reversal of the current 

direction takes place. As the coil moves 
onward, the front half of each coil cuts 
less lines of force than the rear half, in 
ever increasing ratio until the coil arrives 
at a position midway between the two 
pole-pieces where the E. M. F. is a 
maximum, because at that instant every 
line of force cut by the coil is utilized, 
and the induced currents, flowing outward 




WIRES 



:Fig. 59. 

in one half and inward in the other, coincide in direction 
round the coil. 



174 



MODERN ELECTRICITY 



The oerlikon type shown in fig. 59 has a stationary 
armature and a rotary magnet field. The latter consists 
of one solid disk of iron, the circumference of which is 
of a peculiar shape, clearly shown in the cut. The field coil 
is also plainly seen. 



ui \m 








Fig. 60. 

Armature of alternators 

136. As in direct current dynamos, there are ring and drum 
armatures in alternating current machines. 

Fig. 60 shows two diagrams of ring armatures, with the 
difference that in the one on the right the coils are wound 

in opposite directions, and in 
the other they are wound in 
ft the same direction. 

Fig. 61 shows a diagram of 
the connections of an alterna- 
tor armature. The six coils 
represent the coils of the ar- 
mature, and the arrows show 
the direction in which the cur- 
rent flows, from and to the collecting rings and brushes. 

The connection of armature coils may be either in series 
or in parallel, as shown in fig. 62. 




Fig. 61. 



ELECTRICAL ENGINEERING 



175 



Coupling of alternators 

137. Twc shunt-wound continuous current dynamos of 
similar construction may be connected in parallel, and will 




Fig. 62. 



work well together, if they are brought to their usual speed, 
and if their field excitation is adjusted so that they will gen- 




Fig- 63.— Three-phase Motor. 68 revolutions per min. 150 H. P 



176 MODERN ELECTRICITY 

erate the same pressure. The coupling of two alternators is 
not so simple a matter, because, besides the same pressure, 
two other conditions must be fulfilled : first they must be syn- 
chronized, that is, they must be made to have the same 
frequencies exactly, and second, the alternations must be 
co-phasal, that is, their current loops must keep perfect step. 
Two well designed machines will correct each other and 
maintain synchronism. 

Thus, two (or more) alternating-current dynamos may be 
joined up so as to feed a number of lamps simultaneously 
when required, switching out and stopping one when the 
other is able to meet the low demand alone. The armatures 
must be joined up in parallel, not in series, since alternators in 
series are not stable in operating. The machines may be 
driven by belts from the same shafting, or from two indepen 
dent engines running at about equal speed. The latter way is 
generally preferred for economical reasons. 

If an alternator running as a generator, is brought to syn- 
chronism with another, the latter will run as a motor {synchro- 
nous motor). But such a motor will never start itself, as a 
direct current motor does. It must be started by a small 
engine, or other means. Neither can the field magnets of the 
motor be excited from the alternating current circuits. For 
these reasons synchronous motors are not generally used. 
Polyphase currents 

138. In §120 the term phase has been explained by ana- 
logy of the tide in two channels of different nature. Now, 
by having two coils, one of which may be considered wound 
in, half way between the turns of the other, it is possible 
to send two alternating currents around a ring. Then, if the 



ELECTRICAL ENGINEERING 



177 



connections are made as in fig. 64, one wire at A and C, 

the other at B and D, the current waves or loops in one 

wire will be at their height at A 

and C, at the moment when the 

waves in the other wire are at their 

heights at B and D. These waves 

chase each other around the ring, 

keeping perfect step, at a distance 

of one quarter the circle, or 90°. 

This can be proved by adjusting 

a magnetic needle in the center, 

which will rotate at an even gait, following the circling motion 

of the magnetic field, as long as the currents are supplied. 

Fig. 64 shows 
the currents of 

a TWO-PHASE 

system in dia- 
gram. 





I20 ( 
Fig. 



240° 360' 
Fig. 65. 

If three separate windings (see fig. 67) are on the ring, wound 
so that each turn is at the distance of one third of the dia- 
meter of the ring from the correspond- B 
ing turns of the other two, then the 
current phases differ from one another 
one third of the period (120°), as 
shown in fig. 66. Such currents are 

Called THREE-PHASE CURRENTS. 




Fig. 67. 



Polyphase circuits 

139. Alternators designed to furnish 
two or three-phase currents require at least three collecting 
rings, if the currents generated by them are to be furnished to 



178 



MODERN ELECTRICITY 



three wires only. If each of the currents is to be supplied to 
a special wire, four and six rings must be used. 

If the two circuits of a two phase alternator are to be 
kept separate, four wires, A, B, C, D, are required, as shown 
in fig. 68. 




JEL 



EXTERNAL CIRCUIT 



Fig. 68. 



-o- 

8 



One wire may be saved by combining B and C, as shown 
in fig. 69. This arrangement is preferable for long distances, 
because of the saving in copper wire, but the chance of 
trouble increases. The wire B in such a case must have a 
cross section 41 per cent greater than it would have other- 
wise. 

A TRANSMISSION LINES A 




Ht 



B 



B 
EXTERNAL CIRCUIT 
C 



immM 



D 

Fig. 69, KH 

Fig. 70 is the diagram of a three-phase circuit with trans- 
formers (T lt T 2) T 3 ). 

Induction motor 

140. An armature placed in a polyphase or multiphase 
magnetic field will rotate at a uniform speed. The armature 



ELECTRICAL ENGINEERING 



179 



conductors are cut by the lines of force, by which process 
a current is induced in them which causes the armature to 
rotate. Motors operated on polyphase systems are called 
induction motors. They may be used as synchronous poly- 
phase motors. It must be understood, however, that a gene- 
rator and a motor cannot be synchronized exactly, as there 
will be a slight difference in phase, amounting from 1 to 5 
per cent. This difference is called slip, and is due to self- 
induction of the motor. 



THREE 

PHASE 

CURRENT 

GENERATOR 



B 



JTWJ 



Ta 



JTY^J 



T3 



nun 



Fig. 70, 



Sometimes these motors are so constructed that the 
part which causes the induction is stationary. In such 
a case it is more correct to distinguish the parts of an 
induction motor as rotary and stationary, or primary and 
secondary. 

Induction motors are self-starting, and have a considerable 
torque. In practice they are arranged so that a resistance 
may be introduced in their secondary circuit in order to 
prevent too great a rush of current, and to give them full 
torque (see § 115) when starting. 



180 MODERN ELECTRICITY 

Fig. 7 1 shows a diagram of power transmission by means 
of a three phase current. 





GENERATOR FlG - 71 * MOTOR 

Rotary converter 

141. It has been mentioned (see §100) that the currents 
induced in the armature of a dynamo are alternating, when 
the armature is not provided with a commutator, to change 
them into direct currents. If there are two armature wind- 
ings placed on the same core and acted upon by the 
same field magnets, the ends of the windings of the first 
armature being connected to a commutator, and those of 
the other to two collecting rings, alternate currents may be 
drawn off the collecting rings when the machine is run as 
a motor with direct current ; or direct current may be drawn 
from the commutator, if the machine is run as a synchro- 
nous motor with alternate currents. For three-phase alter- 
nating currents, three collecting rings are connected to 
three points that are 120° apart. In a multipolar machine 
each pair of poles must be connected with the rings. 

These machines, used -as the most economical means of 
converting alternate currents into direct currents, or vice versa, 
are commonly called rotary converters. When it is driven 
by direct current and delivers alternating current to the line, 
it is termed an inverted rotary converter ; when so run it has 
features similar to that of a direct current shunt motor. 



CONVERTED CURRENT 



BRUSHES 



THREE PHASE ALTERNATE CURRENT TO 8E 
CONVERTED INTO DIRECT CURRENT 



STARTING 



INDUCTION MOTOR ■ 4 

m \1 





FIG. A. 



THREE PHASE ALTERNATE CURRENT 
TO BE CONVERTED 



CONVERTED CURRENT 
DIRECT 
CURRENT 



BRUSHES 




Fig. 72 — Rotary Converters. 

Fig. A represents a rotary converter with single magnetic field, 
equipped with starting induction motor. 

Fig. B shows a motor generator with two separate fields. This 
machine is, not improperly, called a motor generator, consisting of 
two direct-coupled machines, one of which is run as motor, the other 
as generator. 

181 



182 



MODERN ELECTRICITY 



In order to secure independence of action between the 
motor and dynamo parts of the motor generator, the two 
armature windings are wound upon two separate rings, each 
of them being acted upon by its own field magnet. 

A motor generator has the following disadvantages : It 
is more complicated, considerably higher in price, requires 
much more space, and is less efficient than a static trans- 
former. But it gets out of order very seldom, and demands 
but little care. 

Rotary converters are mostly used, when a direct current 
is to be carried cheaply over long distances. Alternate 
currents are generated and transmitted over the long dis- 
tance to the place of use, where they are converted at will 
into a direct current by means of rotary converters. This 
arrangement is shown in fig, 73. 



ALTER CURRT LAMPS! 



TRANSMISSION LINES 



STATIC 
TRANSFORMER 




ALTERNATOR 



ALTER-DIR-CURRENT CONVERTER 




m 



DIRECT CURRENT LAMPS 



L^EH 



XT" DIRECT 
I I CURRENT LAMPS 



ALT-DIR-C-ROTARY 
CONVERTER 

Fig. 73. 



Static converter 

142. An apparatus, much simpler than the rotary converters 
described in § 141, but doing almost the same service, is the 
static converter, invented by Cooper Hewitt, and first exhi- 
bited in London. January 9th, 1"903. 



ELECTRICAL ENGINEERING 



183 




The static converter, in its present form, consists of a glass 
globe (see fig. 74) about 8 inches in diameter, on the top of 
which there are four glass tubes (1, 2, 3, 4), 
closed at the outer ends and sealed into the 
globe, in which four positive iron-cup termi- 
nals are sealed. Three of these terminals 
(1,2 and 3) serve as connection with the 
three wires of the three-phase current cir- 
cuit, the fourth (4) being connected (only 
when the apparatus is started) for a short 
time to a circuit in which a "kicking" coil 
is inserted. At the bottom of the globe the negative terminal 
(6) is affixed, consisting of a glass cup filled with quicksilver 
which connects to the external circuit by means of a platinum 
wire sealed into the tube. The connection tube (5) on top of 
the globe serves only to exhaust the air from the globe, and is 
sealed off during the process of manufacture. This converter 

permits conversion of single phase or 
polyphase alternate currents into direct 
currents and has, with a weight of 
about 3 pounds, the same capacity as 
a rotary converter weighing about 700 
pounds. A prominent advantage of 
this invention is the fact that there are 
no parts to rotate, so there is no need 
of supervision. Fig. 75 shows a dia- 
gram of connecting the static converter into the circuit of a 
three-phase current generator. The three positive electrodes 
connect to the terminals of the three phase current generator, 
the negative electrode connecting with the external circuit, 




Fig. 75. 



184 MODERN ELECTRICITY 

which returns back to the neutral point of the generator, 
When starting the converter, a current is sent first through 
the globe by means of terminals 4 and 6, to convert the 
quicksilver contained in tube 6 into vapor, filling the globe. 
Then terminal 4 is disconnected, and the main current is 
introduced through terminals 1, 2, and 3. The vapor of 
mercury in the globe permits the positive alternations of the 
current to flow successively from the three positive terminals 
1, 2 and 3 toward the negative terminal 6 The negative 
alternations, owing to a peculiarity of mercury vapor, are 
cut and become inert. 

This converter may be used for voltages ranging from 100 
to 2000 volts, and several similar converters may be worked 
in parallel. The drop in the voltage is constant with- 
out regard to the number of lamps operated by the circuit, 
about 14 volts. 

The loss at 140 volts is about 10 per cent; at 1000 
1*4 per cent. The efficiency of this converter at 1800 volts 
is about 99 per cent. 

Questions and Answers. 

Q. What is frequency? 

A. The number of double alternations per second. 

Q. What frequency is common now in alternating current 
dynamos? A. 60 periods, or 120 alternations, per second. 

Q. What is ohmic resistance ? 

A. It is a term used to distinguish the resistance 
( ohmic r. ) to a steady current from the impedance or 
virtual resistance to simple periodic alternate currents. The 
latter increases with the increase in the rapidity of alter- 
nations and also depends on the form of the conductor. 



CHAPTER X. — Power Station and Electric Railway. 

Faults in machines 

143. In the actual service of electrical machines 
there are a great number of points to be observed, to 
avoid mishaps and accidents. Attention is called here to 
the most important ones. 

If a dynamo fails to generate a current, the fault may 
lie either in the machine or in the external circuit. In 
the machine it may be due to a short circuit in the 
armature or pole pieces, or to poor construction, or a 
broken wire, or a faulty position of the brushes, or a too 
small residual magnetism. In the outside circuit it may be 
due to an open switch, or a broken wire, or burnt-out fuse. 

For the windings of armature and fields the best copper 
wire should be used. It is covered with two or three layers 
of raw cotton thread, which when in place, is varnished 
and baked. Moreover, the wires are insulated from each 
other and from the iron by mica, asbestos, oiled paper 
and other insulators. Notwithstanding the greatest care in 
manufacturing these armature and field windings, the in- 
sulation is broken occasionally by chafing or by heat gen- 
erated by too great a current, resulting in a short circuit 
and burning-out, especially in motors. In such a case, 
the current must be shut off instantly, and the necessary 
repairs made. 

If the mica insulation of the commutator segments is 
injured, the defective place is most easily found by testing 

185 



186 MODERN ELECTRICITY 

each pair of opposite segments by means of a small current, 
from a battery or other source, and a galvanometer, which 
will indicate the faulty spot by a greater fall of potential. 

The commutator must be kept exactly cylindrical, and 
perfectly smooth and clean. It should be wiped with an oily 
rag, but must not be oiled. Flat spots on commutators are 
caused by heat, too much end play, a loose commutator, 
bad belt splice, heavy short circuits on the lines, brushes 
not being set exactly to the diameter of the commutator, 
copper brushes having been welded to their holders, (caused 
by not being pressed firmly enough to the commutator), the 
brush ends being burnt off, or by a heavy overload. The whole 
machine must be kept scrupulously clean and dry, as dirt 
and dampness, even in the smallest quantities, at once render 
the insulation imperfect. 

When an arc on the commutator indicates an open circuit 
(break in the armature winding), a temporary repairing is 
done by connecting the two commutator bars and lead-wires 
where the arc occurs. 

A short-circuited armature becomes heated, but a short- 
circuited field does not. In the armature each turn produces 
a constant E. M. F. ; in the field coil the voltage decreases 
with the resistance. 

If one field coil is short-circuited, it will almost certainly 
burn out its mate, because four times the amount of heat 
will pass through the coil in good condition. 

Practical points 

144. When a compound generator is to be put on an 
already live circuit, four distinct points must be observed: 

First: the generator must be at its normal speed. 



ELECTRICAL ENGINEERING 187 

Second : the rheostat in the shunt windings must be 
adjusted so as to give the same voltage between the ter- 
minals of the generator as in the line. 

Third: The equalizer switch and one of the main switches 
must be thrown in first, and then the second main switch. 

Fourth: the ammeter of the generator must be watched, 
and the field rheostat adjusted, so as to make it take its 
proper share of the load. 

If a generator is thrown in parallel with another generator, 
before its voltage is up to the same point, it will not do its 
proper work, and it may even be run as a motor by the 
stronger current of the circuit. If this happens, the resis- 
tance should be thrown out of this machine. 

When shutting down a generator, running in parallel, these 
points must be observed : 

First : cut down its load, by throwing in resistance in the 
magnetic field with the rheostat. 

Second : open the circuit breaker and then the main 
switches. 

Third : slow down and stop the engine. 

If the shunt circuit is broken, and the other machines 
are not instantly cut off by their fuses melting, the arma- 
tures and series windings of one or more of the generators 
will be burnt out. 

If the bearings get heated, the load should be lightened, 
and if belts are used, they should be slackened, the box caps 
slightly loosened, and more oil put on the bearings, before 
the machine is shut down. If these remedies fail, shut 
down. If the machine is belted, the belt should be taken 
off as quickly as possible, the box caps taken off and a 



188 MODERN ELECTRICITY 

flow of oil kept on the journals while the machine is still 

revolving ; this prevents sticking. Then the linings of the 

bearings should be taken out and allowed to cool in the 
open air. 

When a generator is shut down, great care should be 

taken that the brushes are lifted off the commutator, and 
that all switches and circuit-breakers are open. 

The fault most difficult to find about a generator is a 
short circuit in the armature that takes place only when 
the armature is revolving, but cannot be discovered by the 
detector when the machine is standing still. It is generally 
due to two consecutive armature windings being forced 
together by centrifugal force, or magnetic drag, just at a 
point where a fault in the insulation exists. 

If generators have been standing idle for some time, the 
armature should be thoroughly dried in a regular drying oven, 
if possible, so as to remove any moisture that may have 
settled in the windings, as dampness will most likely cause 
a short circuit, and burn out the armature winding. The 
same result may be reached by putting all the resistance 
of the field rheostat in series with a shunt winding, and 
slowly running the generator on an open circuit, so as to 
attain from a third to half the normal voltage at the term- 
inals, for some hours. When a current from other sources 
is available, the armatures can be fixed so as to prevent 
them from rotating, a heavy resistance put in series with 
them, and a small current run into them, as well as through 
the field windings. 

In putting generators in parallel where the switching 
arrangements of some electric companies are employed 



ELECTRICAL ENGINEERING 189 

the equalizing switch is first closed, then the positive switch 
is thrown in. This throws the series winding of the field 
into parallel with the generator already running. Then the 
field switch is closed. This puts the shunt-winding of the field 
in parallel on the circuit. The generator is then run up to 
full speed, and when the voltage at its terminals is equal to 
the voltage of the line, the negative switch is closed. 

The switchboard 

145. From the generators the electric current passes 
to the switchboard, through conducting cables which connect 
with the main switchboard conductors, commonly called 
omnibus bars, or bus bars. Here are also to be found 
the required switches and meters, starting box, rheostats 
and circuit breakers. See cut on page 191. 

A switchboard must be so placed as to reduce to a mini- 
mum the danger of communicating fire to any combustible 
material. It should be one foot from the floor and three 
feet from the ceiling. It should be made of non-combustible 
material, or of a framework of hardwood, filled in to prevent 
absorption of moisture. 

The meters on the switchboard serve a double purpose, 
to help the engineer regulate the machinery according to 
the service required, and to furnish the manager with the 
necessary facts from which to calculate the expense and the 
value of the plant's work. It is possible to figure the cost 
in labor, fuel, oil and other items, of every kilowatt hour 
generated. It is also possible to keep an approximatively 
accurate account of the output of the plant, by entering 
every fifteen minutes, in a properly arranged book, the read- 
ings of the feeder amperemeters and the volt meters on the 



190 



MODERN ELECTRICITY 



switchboard. Or these instruments may be arranged to make 
their own records. Fig. 76 shows a one day's automatic 
record of an amperemeter. The heavy irregular line indicates 
the strength of the current during the 24 hours, each hour 




Fig. 76. 

being divided into 4 quarters. Each interval between two 
adjacent concentric circles signifies one ampere. A voltmeter 
record is arranged in the same way, except that the distance 
between two circles represents two volts. Exact voltmeter 
records are of the greatest importance. 



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192 



MODERN ELECTRICITY 



The circuit breaker 

146. The circuit breaker is a safety device, which 
automatically opens a circuit when the current exceeds a 
given value. The excess- 
ive current sets up a mag- 
netic force which over- 
comes the power of a 
spring holding two contact 
pieces together, and their 
contact is broken. See 
fig. 78. 

When the contact is 
broken, the inertia of the 
current causes a destruc- 
tive sparking between the 
contact points to obviate 
which several dif- 
ferent means are 
employed. One is 
the magnetic blow- 




out, consisting of an electro-magnet so designed and placed 
that one of the extensions of a divided pole-piece is fixed 



ELECTRICAL ENGINEERING 193 

opposite every point where contact has to be broken. If the 
magnetic lines of force are projected at right angles to the 
spark current, the spark is deflected and practically blown out. 
Other ways of avoiding serious damage are : to let the 
sparking take place between small contact-tips of copper, 
that can be easily replaced ; or to break up the spark into 
a number of small sparks, passing at various points, all 
connected in series. 

Switches 

147. The controlling of high-pressure currents in large 
quantities is a serious matter, and the switches are one of 
the most important parts of a large alternating current station. 
In the most modern plants, the switch contacts are broken 
in oil, each switch being surrounded by a fireproof brick 
casing and worked by the aid of a motor running on an 
auxiliary circuit controlled by the switchboard attendant. 
No high voltage current is brought to the switchboard. In order 
that any section may be insulated in case of a short-circuit, 
the bus-bars are divided into sections. 

A switch, in order to functionate well, should have metallic 
parts of sufficient massiveness to carry the required current 
without opposing any noticeable resistance ; the contact sur- 
faces must be of ample area, firmly pressed together, and 
rubbing against each other, not merely touching. It is not 
well to make the lever-spindle a part of the circuit, as it 
may become insulated through dirt. The best switch is one 
whose arm is forced between two contact blocks, joining 
them. But in breaking the circuit, the arm must be so 
far removed, by a strong spring, from the contact blocks that 
a spark or arc cannot be set up ; as this might cause a 



194 



MODERN ELECTRICITY 



fire, and would certainly soon injure the switch. The base 
of the apparatus should be of pure slate or some equally 
good insulating material, that does not warp, or condense 
moisture readily. The wires to be fastened to the switch 
should be soldered into thimbles or sockets, which are then 

bolted to the 
vi contact blocks. 

7 Fig. 7 9 repre- 
sents a section 
of a standard sin- 
gle knife switch 
designed for 50 
amperes. 

Cut outs 

148. A cut-out 
is a device to 
prevent damage 
to the apparatus 
or to the building in which it is located, from an unduly 
strong current. There are two kinds of cut-outs : those 
actuated by an electro-magnet, and those in which a cur- 
rent of a given strength melts or fuses a piece of wire 
or foil. The best material for a fuse is tin, because it is 
very durable, and melts at so low a temperature. 2359 C, 
that it cannot kindle a fire. The fuse must be long 
enough so that the heat generated in it by the excessive 
current will not too readily be conducted or radiated away 
by the screws holding its terminals in place. The size of 
a fuse, in general, depends on the size of the smallest 
conductor it is to protect. 




Fig. 79. 



ELECTRICAL ENGINEERING 195 

The fuse is generally placed within, or at least mounted 
on, glazed porcelain so as to avoid any danger from the 
melted metal. For heavy currents a number of small fuses 
in parallel are frequently used. In spite of every precaution, 
a fuse is necessarily always a source of danger, and is, 
at best, a clumsy device. They should not be used any 
more than absolutely necessary. 

A magnetic cut-out consists of a solenoid and an arma- 
ture to which a horseshoe-shaped copper rod is attached, 
the two ends of which are immersed in two cups of mercury, 
thus completing the circuit. When the current strength rises 
beyond a fixed point, the armature is drawn into the solenoid, 
lifting the copper rod out of the mercury, breaking the circuit. 
Circuit breaker described in §146 serves the same purpose. 

The starting box 

149. The best type of starting box has cut-out devices 
for both excessive current and no current. The starting 
lever returns automatically to the cut-out position, whenever 
the current attains a dangerous strength, or falls to zero. 
The former takes place when the motor is overloaded, and 
when the difference of potential becomes very low ; when 
the current is broken, either purposely or by the blowing 
of a fuse ; and when the magnetic circuit is broken. 

Lightning arrester 

150. Each wire of every overhead circuit must have a 
lightning arrester near its connection with the station ; and 
also at intervals over the whole system, in such numbers and 
at such places as to prevent ordinary discharges from entering 
(over the wires) buildings connected to the lines. A lightning 




196 MODERN ELECTRICITY 

arrester (see diagram, fig. 80) must be mounted on a non- 
combustible base, and so constructed as not to maintain an 
arc after the discharge has passed. It 
connection must have no moving parts, must be 
readily accessible, away from combustible 
materials, and as near as practicable to 
the building it protects. All sharp bends, 
coils and kinks in the wires between the 
arrester and the outdoor lines must be 
ground avoided as far as possible. It must be con- 
nected with the ground directly (not by a 
gas pipe), straight and permanently, by 
metallic strips or wires of a conductivity not less than that of 
a No. 6 B and S gauge copper wire. The ground wires must 
not be put into iron pipes, as these would tend to impede 
the discharge. Choke coils are often introduced between the 
arresters and the dynamo. 

Electric railway 

151. Siemens and Halske built the first short electric rail- 
way, in Berlin 1879. From that time until 1888 many 
scientists and engineers studied the problem, before a really 
serviceable electric motor car could be constructed. But 
since then, numerous successful systems of electric traction 
have been devised. The electric service therefore has nearly 
replaced all others in street cars. The plate opposite shows 
the electrically important parts of an electric motor car, and its 
connections with the dynamo, in diagram. Fig. 81 is a 
diagram of a street railway line. 

The E. M. F. commonly used on electric railways is 600 
volts. A shock from such a wire is not deadly to man 



198 



MODERN ELECTRICITY 



and this pressure may therefore be carried in bare overhead 
wires. If the system is very extensive, as in large cities, high 
pressure alternating currents are generally employed, which 
are then, at sub-stations, converted by means of rotary con- 
verters to direct current. 




Fig. 81. 

Most traction motors are designed for direct currents. They 
are iron clad to protect them from dirt and especially from the 
water splashed by the wheels in rainy weather, The arma- 
tures are of the type shown in fig. 48, Two motors are 
usually combined on a heavy truck, one geared to each axle ; 
heavy cars in large cities at present usually are equipped with 
four motors. In order to secure a firm grip on the rails, as 
well as to render the whole structure strong and able to stand 
the exceedingly hard service, the truck, wheels and motors are 
built very heavy, Short cars have one truck with four wheels, 
long cars have two such trucks. 

The trolley 

152. The overhead trolley wire far surpasses all other 
means for transmission in electric railways for convenience 
and inexpensiveness, although the numerous poles and wires 
are not sightly and may be a hindrance to the fire depart- 
ment in the case of a fire. The path for the returning 
current is through the rails, the ends of which are electrically 



ELECTRICAL ENGINEERING 199 

Joined together by bonds, short pieces of thick copper wire, 
riveted into holes provided for this purpose. (See p. 197.) 
Or, the two ends of each rail are connected by bonds to 
a copper wire lying between the rails. The conductor con- 
sists of a hard drawn copper wire, over a third of an inch in 
diameter, suspended at frequent points throughout its length 
from insulators which in their turn are supported either from 
horizontal arms projecting at right angles from poles erected 
at the side or middle of the roadway, or from span-wires, 
stranded galvanized iron or steel wire rope stretched between 
poles, one on each side of the road. Connection between 
the wire and the car is made by means of the trolley, 
a deeply grooved, insulated wheel of brass or gun-metal, 
pressed against the wire by a powerful spring, A flat spring 
rubs against the wheel, and passes the current to an insulated 
wire which runs inside the hollow trolley pole to the con- 
trolling switch, (see fig. 156.) 

Other systems are the underground trolley or plough, the 
storage battery, and third-rail systems. In the latter, a shoe 
sliding on a third rail takes from it the current and trans- 
mits it to the controller and motors. It may be raised from 
the rail by a short lever in the controller room, thus breaking 
the circuit. 

The controller 

153. The controller (see fig. 82) is a resistance box, 
put in series with the motors, which are joined in parallel. 
When the car is to be started, a slight turn of the main lever 
switches the car into the circuit with high resistance. By 
turning the lever further, this resistance is gradually cut out, 
as the speed of the car is to be increased. Another switch 



200 



MODERN ELECTRICITY 



on the apparatus is used for breaking the circuit, or reversing 
the motors. In another type the speed is controlled by naving 
the motor fields wound in three or 
more separate divisions and by connect- 
ing these divisions in various combina- 
tions: at starting all in series, at full 
speed all in parallel, and between these 
two points in five or six other interme- 
diate arrangements. 

As the torque (see § 115) at starting 
Is considerable in motor cars, and as it 
may easily happen that a number of 
cars on a line start at the same 
moment, the sudden increase in the 
load, or current required, at such a 
moment may be very great. This in- 
crease, however, has been diminished 
by arranging the controller in such a <L~M>' 

way that the two motors of a car at FlG ' 82 - 

starting are in series. In this way they take but half 
current they would otherwise require. 

Heavy service 

154. Electric locomotives are used to some extent on ele- 
vated roads, in long tunnels, and in many other cases where the 
smoke of ordinary steam engines is objectionable, or where 
great power is required and water power is to be had cheaply. 
Notable examples are the elevated railroads of New York and 
Berlin, the tunnels under the cities of Chicago and Baltimore, 
the underground Central London Ry., the South London Ry., 
Eng., and on the New York, New Haven and Hartford Ry. in 
this country, with an operating voltage of 1 1 ,000 volts- 




the 



ELECTRICAL ENGINEERING 



201 



Several firms have built electric locomotives capable of 
pulling a heavy passenger train over 100 miles an hour, but 
under present conditions, this speed would involve too great a 
danger on surface lines, while an elevated track would have to 
be constructed of solid masonry to stand the strain. 




Fig. 83. 



Fig. 83 shows a Baldwin-Westinghouse electric locomotive, 
for tunnel service. Dimensions: Gauge, 2 ft ; motors, two, 
220 volts; wheel base, 2 ft. 7 ins ; diameter of drivers, 28 
ins.; journals, 3JX 5 ins.; width, 3 ft. 5 ins.; height, 3 ft. 6 
ins.; length 9 ft. 3 ins.: weight, 11,000 lbs. 



a. 2 

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202 



CHAPTER XL — Transmission and Distribution. 



Two=wire system 

i55« The distribution of a light constant current does not 
offer any difficulties, but where a constant potential is required, 
as in a set of lamps, the problem may indeed be a difficult 
one. Usually, as shown in § 128, a small current at high 
pressure is transmitted to points where, by means of trans- 
formers, the pressure is reduced to the desired values, But 
this system demands a very expensive insulation, and a con- 
stant running of dynamos, and besides, the iron loss by eddy 
currents, hysteresis and heating in the transformers and the 
mains is the pos „_ 

v~y S «!> * 



4§> 



NEG. 



2 WIRE INC. SYSTEM 



Fig. 85. 



same, whether 
the secondary 
circuit is at no 
load or at full 
load. Small as this 
loss may be in itself, 
it amounts to a con- 
siderable waste in the 
course of a day. 

Fig. 85 shows a 
diagram of a two-wire system of 1 10 volt incandescent lamps, 
in parallel, supplied by a direct current dynamo. Fig. 86 is 
a diagram of the same system with lamps in series. 

If the continuous current is led directly from the dynamo 

to a number of lamps joined in parallel, it is impossible to 

regulate the difference of potential. The nearest lamp will 

203 




204 MODERN ELECTRICITY 

have a higher difference than all the others, and the farthest 
lamp will have a lower one than all the others, Thus it 
would become necessary to use different types of lamp, 
and even such an arrangement would not work, unless all 
the lamps were burning all the time. One way out of 
this difficulty would be to have as many wires as lamps, 
or to use a smaller wire for each following lamp. Another 
method is to have subsidiary feeders, connecting the dynamo 
with various points in the circuit directly. The regulation 
of the pressure is made possible in such case by thin 
pilot wires, connecting the nearest and the most distant 
lamp terminals with a voltmeter in the power station. 
Usually, one or more storage batteries, joined in parallel 
with the dynamo, are switched in or out temporarily, when 
the voltmeter indicates a fall or rise of potential 

Three=wire system 

156. Not more than two incandescent lamps are generally 
placed in series, because the breaking of one filament 

„ in a set would extinguish all 
the lamps of that set. The 
employment of groups of 
_ two lamps in series is made 
convenient by the three- 
wire system, in which two 
m equal dynamos are used, 
joined in series, so that the 
positive terminal of one is 
joined by the positive main conductor and the negative termi- 
nal of the other is connected to the negative main. The 
lamps are placed in groups of two irv series across the two 




THREE WIRE SYSTEM 

Fg. 87 



ELECTRICAL ENGINEERING 205 

mains, and a thinner third wire runs from the junction of the 
two dynamos across the junctions of each group of two 
lamps. See fig. 87. 

When the number of lamps on both sides of the third 
wire is equal, there will be no current either way in the 
third wire. If one lamp is cut out on the positive wire 
side, the potential will fall in the third wire, because the 
resistance between the positive wire and third wire becomes 
greater. As the potential at the junction of the two 
dynamos has remained unaltered, a current will flow from 
that point through the third wire, supplying the extra lamp 
on the negative side. On the other hand, if a lamp is 
cut out on the negative side, the potential of the third 
wire is raised, and a current will flow toward the junction 
of the two dynamos. If lamps are burning on one side 
only, and none on the other side, the dynamo on the other 
side will do no work, while the neutral wire will act as 
positive or negative main, according as the working dynamo 
is connected to the negative or positive main wire. 

When the same number of lamps is supplied on both 
sides, the system is said to be balanced. In such a case 
the third wire may be quite small. The less the system 
is balanced, the larger must be the third wire. It should be 
of the same size as the mains, when the whole set of 
lamps on one side is cut out, because in that event it 
must carry the whole current. Pilot wires are used, con- 
necting each point to two separate voltmeters. 

This system amounts practically to connecting the lamps 
in series, and still making them independent of each 
other. It may be extended to five wires, with 4 dynamos 



206 MODERN ELECTRICITY 

supplying groups of 4 lamps in series, but such methods 
of distribution are economical only where the area to be 
supplied is very extensive. 

One secondary battery may also be used, connected in 
series with one of the dynamos, in order to dispense with the 
other generator, or two batteries together with the dynamos, 
connected in parallel with them. Or subsidiary machines, 
called boosters, are employed to maintain the pressure in 
the feeders, or at certain points. See § 131. 

The wire 

157. In this country uniformity was brought into the 
rules for wires, insulation, etc., by the National Electrical 
Code of 1903, the result of the united efforts of the various 
insurance, electrical, architectural and allied interests. This 
code contains detailed rules and requirements for the installa- 
tion of electiic wiring and apparatus, and every electrician 
should possess a copy. 

In overcoming the resistance of a conductor electrical 
power is wasted, which means expense. Economy therefore 
demands a reduction of resistance to a minimum. But as 
enlarging the size of wire, also, means expense, it is 
acknowledged as a rule, that the size of a conductor must not 
be so large that the additional expense will more than balance 
the cost of the power saved. The cost of the energy 
wasted in heating the conductors should not be more than 
the interest on their original cost. On the other hand, a 
conductor should never be so small that the maximum cur- 
rent to be transmitted can appreciably raise its temperature. 

If one of two round wires has double the diameter of 
the other, its sectional area is four times as large, and so 



ELECTRICAL ENGINEERING 207 

is its conductivity, but its circumference (surface) is only 
doubled. This means that the heat generated will be qua- 
drupled, if a current four times as great passes, while the 
radiation is only doubled. Consequently the thicker wire 
will show a higher temperature. As the presence of any 
foreign matter increases the resistance of a conductor enor- 
mously, it is economical to use the purest copper obtainable. 

Proper size of wire 

158. A pure copper wire, one foot long, and of a cross 

section of one circular mil has a resistance of about 10-8 

ohms at 75° F. (See § 56.) Consequently the resistance of 

any pure copper wire may be expressed by the formula 

R = 10-8 L-^-C. M. or, in words, 

RULE 42. -The resistance of a pure copper wire is equal 
to 10' 6 times its length in feet, divided by its cross section in 
circular mils. . 

The drop in pressure (loss of volts, K) of a current / 

in a conductor with the resistance R, according to Ohm's 

law is V= R I 

therefore, V= 10-8 L I-+-C. M. 

and C. M. = 10-8 L l-*-V or, in words: 

RULE 43. — The circular mils in the cross section of a 
pure copper wire must equal the specific resistance times the 
length in feet times the current in amperes, divided by the 
drop in volts. 

This drop is determined by the pressure at the source 
(dynamo or battery,) and that percentage of pressure which 
may reasonably be lost in transmitting. If the pressure at 
the dynamo is 150 volts, and the loss is 10 per cent, then 

the drop is 1 5 Volts. (Continued on page 210.J 



208 



MODERN ELECTRICITY 



PROPERTIES OF BARE COPPER WIRE. 















Birmingham 






Brown 


& Sharpe Gauge. 




or Stubs 
Gauge. 




Diameter 


Diameter 


Area 


Weight 


1 

Resistance 






s 


in parts 




in circular 


in pounds 


in ohms 


Diameter 


3 


of 


in mils. 




per 


per 1000 ft. 


in mils. 


z 


an inch. 




mils. 


1000 feet. 


at 60° F. 




oooo 


.46 


460. 


211 60O 


624. 


.048 


454 


ooo 


.4096 


409.6 


167 800 


546, 


.061 


425 


oo 


.3648 


364.8 


I33 IOO 


437. 


.076 


380 


o 


.3249 


324.9 


105 500 


35°. 


.096 


340 


I 


.2893 


289.3 


83 690 


272. 


. 122 


3°o 


2 


.2576 


257.6 


66 370 


244. 


.153 


284 


3 


.2294 


229.4 


52 630 


203. 


.194 


259 


4 


.2043 


204.3 


41 740 


172. 


.245 


238 


5 


.1819 


l8l. 9 


33 100 


146. 


.307 


220 


6 


. 1620 


162. 


26 250 


124. 


.388 


203 


7 


.1443 


144.3 


20 820 


98. 


.491 


180 


8 


.1285 


128.5 


16 510 


82. 


.621 


165 


9 


.1144 


1 14. 4 


13 090 


66. 


.783 


148 


IO 


. IOI9 


101 .9 


10 380 


54. 


•979 


134 


ii 


.0907 


90.74 


8 243 


43. 


I .229 


120 


12 


.0808 


80.81 


6 530 


35. 


1.552 


109 


13 


.072 


71.96 


5 178 


27. 


I.964 


95 


14 


.0641 


64.08 


4 107 


21. 


2.485 


83 


IS 


.0571 


57.07 


3 257 


15. 


3.133 


72 


16 


.0508 


50.82 


2 583 


12. 


3.9H 


65 


17 


.0453 


45.26 


2 048 


10. 


5.028 


58 


18 


.0403 


40.3 


1 624 


7-3 


6.363 


49 


*9 


• °359 


35.89 


1 288 


5-3 


7.855 


42 


20 


.032 


31.96 


1 022 


3-7 


9.942 


35 


21 


.0285 


28.46 


810 1 


3-i 


J2.53 


32 


22 


• °253 


25.35 


642 4 


2.4 


15.9 


28 


23 


.0225 


22.57 


509 5 


i.9 


19-93 


25 


24 


.0201 


20. 1 


404 


1-5 


25.2 


22 


25 


.0179 


17.9 


3204 


1 .2 


3L77 


20 


26 


.0159 


15.94 


2598 


1 .0 


40.27 


18 


27 


.0142 


14.2 


201 5 


0.7 


5o.49 


16 


28 


.0126 


12.64 


1598 


0,6 


64.13 


14 


29 


.0113 


II .26 


126.7 


0.51 


79.73 


13 


30 


.01 


10.03 


100 5 


o.43 


101.8 


12 


31 


.0089 


8.93 


79 7 


0.30 


128.5 


IO 


32 


.0079 


7.95 


63.21 


0.24 


159. 1 


9 



ELECTRICAL ENGINEERING 



209 



In studying the table on page 208 it will be seen that the 
weight and area about double with every three numbers. For 
instance, No. 11 weighs 43 lbs. per 1,000 feet, No. 8 weighs 
82. No. 5 100, No. 2 244, No. 00 437. 



TABLE OF SAFE CARRYING CAPACITY OF INTERIOR 

WIRES. 



Size of Wire, 


Circular Mills. 


Current in 


Amperes. 


B. & S. Gauge. 


Rubber Insulation. 


Other Insulations. 


14 


4,107 


12 


16 


12 


6,530 


17 


23 


IO 


10,380 


24 


32 


8 


16,510 


33 


46 


6 


26,250 


46 


65 


5 


33> IO ° 


54 


77 


4 


41,740 


65 


92 


3 


52,630 


76 


no 


2 


66,370 


90 


131 


I 


83,690 


107 


156 


o 


105,500 


127 


185 


oo 


133,100 


150 


220 


ooo 


167,800 


177 


262 


oooo 


211,600 


210 


312 


300,000 CM. 


300,000 


270 


400 


500,000 CM. 
1,000,000 CM. 
2,000,000 CM. 


500,000 
1,000,000 
2,000,000 


390 

650 

1,050 


590 
1,000 
1,670 



Wire smaller than No. 14 is never used except for wiring 
metal fixtures of incandescent lamps. 

For aluminum wire the safe carrying capacity is 84 per 
cent, of that in the above table. 



210 MODERN ELECTRICITY 

EXAMPLE 68. 

A current of 80 amperes is to be transmitted over a 
wire 800 feet long with a drop of 10 volts in pressure. 
What size of wire is required ? 

C. M.= 10-8X800X80-^- 10=69,120 According to the 
table on page 208, a number 2 wire, B and S gauge. Ans. 

EXAMPLE 69. 

Two arc lamps connected in parallel require 6 amperes 
each at a pressure of 90 volts. The positive and negative 
wire are each 2500 feet long. The voltage at the dynamo 
terminals is 95 volts. What size of wire is required ? 

C M. = 10-8 X 5000 X 12^-5 = 129,600 According to 
the table on page 208, a number 00 wire, B and S gauge. 
Ans. 

RULE 44. — The cross section of a wire is in inverse pra 
portion to the square of the pressure. 

Explanation: The weight of copper required to supply, 
at a fixed percentage loss of pressure, a given number of 
100 volt lamps, will supply four times as many lamps at 
double -the pressure and the same distance. And at a pressure 
of 300 volts, the same wire will supply nine times as many 
lamps. 

Wire tests 

159. Hard-drawn copper wire is subjected to a double 
test, that of bending and that of twisting. It must be capable 
of being wrapped in six turns around wire of its own diameter, 
unwrapped, and again wrapped in the same manner and 
direction, without breaking. A piece of say six inches is 
gripped between two vises, one of which revolves at a speed 
not exceeding one revolution per second, and each wire of a 
certain diameter must stand a given number of twists without 



ELECTRICAL ENGINEERING 



211 



breaking. An ink mark the length of the wire shows in a 
spiral on the twisted wire, indicating the number of twists. 
Galvanized iron telegraph wire must be soft and pliable, 
capable of elongating 15 per cent without breaking. It must 
not break under a strain less than two and one half times 
its weight in pounds per l.iile. In the test for ductility, a 
piece of six inches must stand being twisted between two 
vises 15 revolutions without breaking. At 68° F. t the elec- 
trical resistance in ohms must not be greater than the quo- 
tient arrived at by dividing the constant number 4800 by 
the weight of the wire in pounds per mile. For each degree 
F. above or below 68°, the coefficient -003 is allowed. The 
galvanizing is tested as follows : The wire is plunged into 
a saturated solution of sulphate of copper for one minute, 
then taken out and wiped clean. This is done four times. 
If the wire has a copper color after the fourth time, it 
is a proof that the iron is exposed and that the zinc was 
too thin. The wire must show black. 

Insulation 

160. An electric 
current returns to its 
source by the easiest 
possible path, or along 
the line of least resis- 
tance. 

The ground , 
whether earth or lake 
or sea, always affords an easy and the shortest path back 
to the source, and in order to compel an electric current 
to flow through all the parts of the circuit in undiminished 




Fig. 88. 



212 MODERN ELECTRICITY 

force, provision must be made against any portion of it 
taking a short circuit, that is returning to its source through 
the ground. In fig. 88 imperfect insulation of a telephone or 
telegraph conductor causes portions of the current to short- 
circuit down the poles P P P, and return to the source 
through ground plate A. 

It might be argued that the expense of the negative wire 
could be saved by connecting the end of the positive wire to 
the ground, and likewise the negative terminal of the dynamo 
or battery, as shown in the diagram. It is done in telegraphs 
and other apparatus where a very small current is required. 
A ground plate buried in the earth is connected with the 
positive wire and another with the negative dynamo brush. 
But where a large current or a very high pressure is 
employed in buildings and must be kept under constant 
control, nothing is safe except an arrangement by which 
every part of the entire circuit can be perfectly watched 
and easily reached. 

All conductors exposed to possible contact with the ground, 
directly, or indirectly through a good conductor, must be 
insulated, that is, covered with damp-proof, water-proof, 
non-conducting material. Moisture is the thing mostly to be 
avoided, as many materials that are good insulators, lose 
this quality if water can affect or penetrate them. It has 
been found impossible to keep dampness out of any empty 
space under ground. 

Paraffine oil, even in a very thin film, is a damp-proof 
insulation ; so is India rubber. Guttapercha is practically 
imperishable, if not exposed to light and air, but it softens 
at a low temperature, and the wire would sink through it 



ELECTRICAL ENGINEERING 213 

if heated by the current. Vulcanized rubber cannot be used 
on bare copper because of the sulphur it contains, the copper 
must be heavily tinned. A more economical material than 
any of these consists of fibre impregnated with an insulating 
oil. It is generally sheathed in lead, to protect it from 
both moisture and mechanical injury. See § 162. 

Overhead wires 

161. Where the difference of potential between the posi- 
tive and negative conductors is less than 300 volts, as in the 
ordinary three-wire system, bare overhead wires are perfectly 
safe. Beyond this voltage, at least in cities and towns, it 
is customary to insulate the wires, generally with three 
layers of braided cotton soaked in some insulating and weather- 
proof compound. A No. 6 B and 5 gauge wire so insulated 
carries safely over 2000 volts, when the current is small, as 
in an arc-lamp circuit,, where it rarely exceeds 10 amperes. 

Since dry air is a non-conductor, bare copper wires strung 
at a certain distance from the ground, will carry a strong 
electric current without leakage. The cheapness in construc- 
tion is not the only advantage of the system of placing the 
conductors overhead. It affords, also, great facilities for 
inspection and repair, and for extension. Wherever, therefore, 
the voltage is not exceedingly high, and where the con- 
ductor is not too massive, the overhead system is employed 
whenever local conditions permit it. It is very appropriate 
for a series circuit of arc lamps requiring a constant current 
of not more than about 10 amperes. The size of the wire 
depends more on mechanical than on electrical necessities. 
For instance, a wire No. 10 B and 5 (Brown and Sharpe 
gauge) would safely carry the above mentioned current of 



214 MODERN ELECTRICITY 

10 amperes, but usually a much heavier wire, No. 8 cr 7, 
is used to stand the strain, which is very severe in a gale. 
Such wires must be made of hard drawn copper, which is 
now produced, with a breaking weight of about 30 tons 
per sq. inch, from pure copper, with an increase of elec- 
trical resistance of not more than two per cent. 

Bare wires are supported on glass or porcelain insulators 
fastened to poles of iron or wood. The porcelain must be 
of the best quality, however, because if the glaze is chipped 
or cracked, and the inner mass is not impervious to moisture, 
it loses its insulating properties at once. V/ooden poles 
have the advantage that, in case an -insulator is broken, 
the pole does not shcrt-circuit the conductor as badly as 
an iron pole would. The trunk of a fir or pine, thoroughly 
impregnated with creosote, makes an excellent pole, and 
lasts a very long time. 

Underground circuits 

163. Conductors can be laid underground in many diffe- 
rent ways, in subways, conduits, channels, or pipes. The 
leading principle in all underground work of this kind must 
be perfect insulation and exclusion of moisture. 

A subway is a tunnel underground, of sufficient dimen- 
sions to permit the easy passage of a man. In the tunnel 
the electric cables and wires, also gas and sewer-pipes 
etc., can all find place, and it is easy to reach any spot. 
But the great expense of construction, and the want of 
room are serious objections, and even with the greatest 
care in providing drainage and ventilation, dangerous accu- 
mulations of gases cannot be altogether avoided in a 
subway. 



Electrical engineering 



215 




Fig. 89. 



One kind of conduit is made ot perforated blocks of 
earthenware or wood, six feet long, especially prepared with 
creosote or asphalt, see fig. 89. The 
blocks are laid end to end and jointed 
by a saddle piece of the same material. 
The cables or wires are drawn in by 
means of ropes, from one manhole to 
another. The ropes are preferably 
pulled into the ducts or holes of each block as it is 
laid down in place. 

Another system of conduits consists of troughs or chan- 
nels. One type of these is a rectangular (or semi-circular) 
cast iron trough laid in a trench. The troughing is made 
in six-foot lengths, about a quarter of inch thick, the cross- 
section varying according to the number of cables to be 
placed. Each piece fits into a socket of the next piece 
and is bolted to it, the joint being sealed with bitumen. 
In the trough, at intervals of 2 feet, wooden supports 
(bridges) are placed, treated with bitumen and provided with 
slots into which the cables are laid, so as not to touch 

each other or the iron, 
The trough is then filled 
up with bitumen, and 
covered with an inch of 
concrete or an iron lid. 
This system allows of 
such careful work that 
no repairs need be apprehended under ordinary circumstances. 

A similar system has iron pipes in sections of 20 feet 
each, containing the wires ani finally filled up with some 




Fig. 90. 



216 



MODERN ELECTRICITY 



bituminous insulating material. These pipes are laid about 
30 inches deep, and about 20 inches from the curb 

They are jointed by means of coupling 
boxes, (see fig. 90,) cast iron shells 
made in halves. The bottom half is 
clamped over collars at the tube ends, 
then the three flexible copper stranded 
connectors are forced over the opposite 
wires, and by aid of the plumber's torch 
(see fig. 91) the couplings are heated 
and soldered so that a solid metallic 
junction is formed. Then the upper half 
shell is bolted to the lower one, and 
hot bitumen poured in through the open- 
ing provided for this purpose at the top. 
Fig. 92 represents the kind of coupl- 
ing-box used where a corner is to be turned, and fig. 93 
shows a triple or branch coupling-box for connecting a 
house service with the mains. This method is widely used 
in the three-wire system. 




POCKET BLOW TOUCH 
Fig. 01. 




Fig. 92 



Fig. 93. 



Where a feeder loins the mains, a junction box is sunk 
in the ground, flush with the street level. The conductors 



ELECTRICAL ENGINEERING 217 

and thin tubes enter this box from below. In a three 
wire system, there are three metallic rings provided in the 
junction box, insulated from each other. To one of these 
rings all the positive conductors are connected through fuse 




Fig. 94. 

strips, to the second all the negatives, and to the third all 
the neutral wires. The box is kept watertight by a rubber 
gasket and by an iron cover bolted down. Bitumen is poured 
over the bolts. In fig. 94, the letter A marks one of the 
slabs of insulating material for the pilot wires ; B is a 



218 



MODERN ELECTRICITY 



feeder tube containing five conductors, two positive, two 
negative and one neutral, and also the pilot wires. K K 
are main tubes. 

163. In a third system of underground cable, a layer 
of fibre impregnated, under pressure, with bitumen is laid 
around the stranded core of copper conductors. (See fig. 
95, in which the two small wires separately insulated are 

pilot wires.) The 
layer of fibre is 
about one half as 
thick as the 
strand. Immedi- 
ately after the 
impregnation is 
completed and 
while the bitumen 
is still hot, two 
coverings of lead 
are put on, one 
over the other, 
with the aid of 
hydraulic pressure, 
squeezing the fibre 
into a solid mass. Over this is a layer of jute, treated 
with an impervious compound. A double sheating of iron 
ribbon protects the jute from mechanical injury, and is 
itself protected against moisture by another coating of some 
impervious compound. Such a cable is laid bare in a trench. 
If an iron trough is provided, the iron sheathing, of course, is 
dispensed with, and the pilot wires are laid separately. 




Fig. 95. 



ELECTRICAL ENGINEERING 219 

Tough paper forms an excellent insulating material for 
electric light and power cables, but it must be kept perfectly 
dry, and for this reason is encased in a lead sheathing. 
Such a cable is especially suitable for alternating current 
transmission because of the very low inductive capacity of 
pcper and the air between its crinkles or loose folds, which 
insures a much lower electrostatic capacity than can be 
obtained in any other way except at great expense. 

Wiring buildings 

164. Conductors of electric bell, telephone, or similar 
systems using the current generated by a battery, are not 
dangerous in themselves, but may become so if they are 
improperly crossed by a light or power wire. 

For ordinary wiring for incandescent lamps in buildings 
the very best rubber-covered wire should be used. Great 
care should be exercised in selecting the wire, as there is 
much poor material in the market. Inside wiring which is 
well planned and executed, cannot possibly cause a fire. 

In wiring a building, connection with the street main is 
made through a cut-out. The two service wires end in a 
cabinet located centrally and convenient. In this cabinet 
there are as many fuse-blocks as there are small circuits 
in the building. Each small circuit is separately connected 
with the service wires through a fuse block. This arrange- 
ment is much better, than having the fuse blocks scattered 
all over the building. Of course, in very large buildings 
there may be several such distributing cabinets, as there 
may be, also, several main service wires or feeders, all 
connected to a large special circuit, the crib, from which 
the taps or small circuits radiate. 



220 



MODERN ELECTRICITY 



Where there is no objection to leaving the wires in 
plain sight, as in small shops or stores, they are not covered 
up, and are held in place by means of porcelain knobs 
or cleats. But they must be so placed that they are not 
liable to mechanical injury. An excellent protection is 
afforded by placing the wires in wooden casings or mould- 
ings, nailed to the ceiling or walls, but ' they cannot be 
said to be ornamental. It is no longer permitted to run 
the wires along the walls before the plastering is done, 
and then cover them with plaster. They are easily injured 
that way, and hard to find and reach when in need of 
repair. The best method is to construct in the walls a 
water-tight conduit of iron pipes, enamelled or varnished 

inside, into and out ex 
which the wires may 
be pulled at any time. 

As a precaution 
against moisture from 
rain water, wires must 
have drip loops outside, 
where they enter build- 
ings, and the holes 
through which the con- 
ductors pass must be 
bushed with non-com- 
bustible , non- absorptive 







■lllllllH 



H3 



mv 



Fig. 96. 



insulating tubes, slanting downward toward the outside. 

Electric bells 

165. The common electric bell has a very simple mechan- 
ism. Opposite the poles of an electro-magnet fixed on a 



ELECTRICAL ENGINEERING 221 

board, there is an armature or key (see § 64) attached 
at one end to a spring, and carrying at the other end a 
bell clapper. Ordinarily the spring holds the armature 
lightly against a contact point completing the circuit. 
When the button is pushed in, the current from a cell or 
battery of cells flows through the magnet coils and the arma- 
ture is attracted, making the clapper strike the bell, and at 
the same instant also breaking the circuit by separating 
from the contact point. The current stops, the armature 
flies back against the contact point, the current flows anew, 
the clapper strikes the bell again, and so on in rapid repeti- 
tion, as long as the button is pressed. 

When an electric bell is out of order, the cause may be 
poor contact at the contact point or in the push button. 
This fault is easily remedied by cleaning or scraping. Or 

the contact points may be out of adjustment, or there may 
be a short circuit in the field winding. But usually poor insula- 
ation of the wire is the cause. 

For electric bells so-called annunciator wire is much used, 
a No. 16 B. and S. copper wire insulated with two thick 
layers of cotton, wound in opposite directions, paraffined and 
varnished, but the extra cost of using rubber-covered or 
other weather-proof wire is so small that it is poor economy 
not to use it. 

Faults in wires 

166. Telephone and telegraph wires, being exposed, are 
liable to many injuries, causing faults that may be classified 
as breaks, poor connections, grounds and crosses. A line is 
said to be dead grounded, when the leakage is large enough 
to render impossible the proper use of the conductor. The 



222 MODERN ELECTRICITY 

leakage may take place at one place, or may be distributed 
over a number of places. Two lines are said to be crossed, 
when sufficient current leaks from one to the other to inter- 
fere with their proper working. A break will cause the arma- 
tures of the relays to fall back from their magnets. A poor 
connection may be due to a working loose of the wire 
or the binding screw, or to corrosion, a thin film of which 
will seriously increase the resistance. For this reason joints 
of wires must be made very carefully. The two ends are 
generally well cleaned, wound tight around each other and 
then covered with solder, in order to exclude any moisture 
that would cause corrosion. 

An experienced telegraph operator will notice instantly a 
variation from the wonted distinctness of the signals. If 
this lack of distinctness is the same on both ends of a 
line, it must be the fault of the battery, or of poor con- 
nections. If the battery is at one end, and the incoming 
signals are fairly strong, but the outgoing signals are weak, 
it is clear that the outgoing current is weakened by too 
much leakage, while the incoming current through the ground 
has no such fault. See fig. 88, page 211, in which A marks 
the groundplate of the battery station and B the other 
If it is possible to signal over a part of aline only, there 
is a break beyond the last station to which signals can 
be sent, and the broken end of the wire is grounded. 

Line testing 

167. All new lines should be carefully tested, as explained 
in the following paragraphs. When a test discloses a ground, 
coss or break, but does not locate it, as in a large system 
of incandescent circuits, one branch after another is cut 



ELECTRICAL ENGINEERING 223 

out, until the fault is no longer noticed. It can then be 
found in the branch last cut out. 

Direct electrical measurement is employed for testing 
the conductivity of long distance telegraph and telephone 
lines. Where two wires can be used for testing, both are 
connected at one end, and at the other end they are con- 
nected to a Wheatstone bridge and a sensitive galvanometer, 
(at points O and M of fig. 33, page 115) The two wires 
being of equal size and length, one half the resistance shown 
by the test pertains to each wire. Where there is one wire 
only, the further end is grounded, the near end is connected 
to point O or M of the br.dge, and M or is connected 
with the ground. If the ground connection is perfect, the 
resistance indicated is that of the wire, except at times 
when the ordinary electrical condition of the earth is dis- 
turbed by magnetic storms. 

The individual resistance of three or more wires on one 
line is easily found by establishing that of each pair of 
them. If, for instance, wires a and b together show 1200 
ohms, wires b and c 1500, and a and c 1700, then all three 
wires together have a resistance of 2200. 



a+b = 


■■ 1200 


b+c = 


1500 


a+ c = 


1700 



Add: 2a + 2b + 2c = 4400 

Divide by 2: a+b + c = 2200 

By subtracting a + b from 2200, c is found = 1000 
By subtracting b-rc from 22C0, a is founds 700 
By subtracting a+c from 2200, b is found = 500. 



224 MODERN ELECTRICITY 

In § 93 it has been shown how insulation measurements 
are made, when the insulation resistance is higher than 
could be measured by a Wheatstone bridge. For ordinary 
purposes, and especially in the daily measurement of the 
conductivity of a long distance telegraph or telephone line, a 
milliamperemeter placed in series with the battery at one 
end of the circuit will suffice. The proper resistance of 
the circuit being known, also the E. M. F. of the battery, 
a simple comparison with the daily entries of the readings 
will show the amount of leakage. 

Locating a ground 

168. A dead ground is easily located by dividing the 
resistance of line and ground return by the known number 
of ohms for the whole line. If the whole line of 1000 
miles usually shows a resistance of 10,000 ohms, or 10 
ohms per mile, a resistance indicated by the bridge at 
6500 ohms would prove that the fault is 650 miles from 
the station. 

If the ground is only partial, the method of calculating the 
distance at which the fault lies from a station, is more 
involved. To the known resistance of the line (say 3500 
ohms), when in good order, is added the resistance (4500), 
indicated by the bridge, through the fault from one station, 
the other end being open. From this sum (8000) is sub- 
tracted the resistance (4100) through the fault from the 
other station, measured by the bridge, with the other end 
open. In this way the line resistance and the leak resis- 
tance are both counted twice, and by dividing the difference 
(3900) by two, the resistance of the line from the first 
station is found. Dividing this figure (1950) by the ohms 



ELECTRICAL ENGINEERING 225 

per mile (say 10 ohms,) gives the distance in miles (195) 
of the fault from the first station. 

The methods described here are also employed for testing 
and locating faults in underground cables. 

A cross of two wires is located by using them as one 
circuit, measuring their joined resistance along one wire 
through the cross and back along the other wire, and divid- 
ing this quantity by the sum of the known individual resis- 
tances of ihe two wires per mile. The result is the distance 
of the cross from the station. 

Lineman's detector 

169. A handy instrument for localizing faults or tracing 
circuits is the so-called lineman's detector, consisting of two 
common spools mounted vertically and wound with two 
coils of wire, one consisting of a few turns of thick wire 
having 0*2 ohm resistance and the other of many turns of 
fine wire with a resistance of 100 ohms. The magnet, about 
an inch long, is mounted on a horizontal axis, which carries 
also the long non-magnetic pointer playing over a scale. 
Each coil is connected with one end to one of two terminals, 
the other ends being both connected to a third terminal, 
A current from a single Daniell cell, of about 10 milli- 
amperes, flowing through the thin-wire coil, deflects the 
pointer about 45°; a current of 150 milliamperes from the 
same cell, flowing through the switch-wire coil, causes a 
deflection of about 25°. 

Magneto bell 

170. Another practical device is the magneto bell, used 
for arc-light and other series circuits, which are in use dur- 



226 MODERN ELECTRICITY 

ing a part of the day only. As the name implies, it has a 
call bell and a magneto in a small portable box, connected 
in series with the two terminals. After the two ends of a 
line are connected with the terminals, a crank is turned ; 
and if the bell does not ring, this is a proof that the cir- 
cuit is broken. When one terminal is connected with the 
ground through a water or gas pipe, and the other terminal 
with the line, the. turning of the crank will cause a lively 
ringing of the bell if the line is grounded. 

The tests described in § 169 are employed during the time 
when the line is not in use. When in use, an arc-circuit may 
be tested for a ground by connecting in series as many incan- 
descent lamps as there are arc lamps, and of the same 
resistance, between one terminal of the dynamo and the 
ground. Then, if one incandescent lamp after the other is 
cut out, until those remaining show full candle power, 
their number is the same as that of the arc lamps between 
the dynamo and the fault. The same result can more 
simply be obtained by connecting a voltmeter between one 
dynamo terminal and the ground. Dividing the voltage 
indicated by the pressure required by each lamp, gives the 
number of the lamps on the near side of the fault. 

Ground detector 

171. A ground of one wire in a two-wire incandescent 
circuit may be shown by a single incandescent lamp con- 
nected, by a switch, between the other wire and the earth. 
The current flowing through the ground will cause it to 
burn, the brighter the more nearly dead grounded the faulty 
wire is. Such a lamp is called a ground detector. A 
voltmeter connected in the same manner instead of such 



ELECTRICAL ENGINEERING 227 

a lamp will show full pressure at dead ground, and zero 
at no ground. Two lamps may be used' between which a 
connection by a switch is made to the earth. Each lamp 
is connected to one conductor. If either wire is grounded, 
the lamp connected to the other wire will burn brighter 
than the other one, when the switch is closed. For three- 
wire systems one such pair of lamps is used for each side. 

Questions and Answers. 

Q. What is a metallic circuit? 

A. One in which wires are used for both outgoing and 
return conductors, as distinguished from a grounded circuit. 

Q. Suppose there are 20 lamps burning on one side 
(A) of a three-wire system, and 42 lamps on the other (B), 
each lamp taking £ ampere, what would be the result? 

A. Dynamo A would return 10 amperes through the 
neutral wire ; dynamo B would send 21 amp. out through it ; 
therefore, a current of 11 amp. would flow out. (21 — 10=11.) 

Q. What is meant by low and high potential? 

A. In a low-potential system less than 550 volts are carried, 
in a high-potential from 550 to 3500, and in an extra-high- 
potential over 3500. 

Q. How could a single stroke bell be made out of an 
ordinary vibrating electric bell ? 

A. By omitting the contact point back of the armature, 
and connecting the two magnet coils directly with the bat- 
tery, leaving the armature and spring out of the circuit. 

Q. When was the electric bell invented, and by whom ? 

A. In 1830, by Professor Joseph Henry of the Smithsonian 
Institute, Washington, D. C. See § 78. 



CHAPTER XII. — Electrical Lighting 

The Voltaic arc 

172. The electric arc was discovered by Sir Humphry 
Davy, the famous English scientist. In 1808, during a lecture 
before the Royal Institution in London, he employed 2000 
primary cells, connected to two little rods of light-wood 
charcoal, an inch long and one sixth as thick. When 
these were brought near each other, point to point and 
horizontally, (within the thirtieth or fortieth part of an 
inch) a bright spark was produced, and more than half the 
volume of the charcoal became ignited to whiteness ; and 
by withdrawing the points from each other, a constant dis- 
charge took place through the heated air in a space equal 
to at least four inches, producing a most brilliant ascend- 
ing arch of light. Any substance introduced into the arch 
became incandescent : platinum melted like wax in the 
flame of a candle; sapphire, magnesia, lime were fused. 
The explanation is that the space between the two points 
was filled with carbon vapor, which is a much better con- 
ductor than the air, that the current passing through the 
vapor rendered it luminous, and that the arched form was 
caused by the upward rush of the heated surrounding air. 
The name "arch" or "arc" has remained, although the 
light takes a different shape when, as in modern arc-lamps, 
the two pieces of carbon are vertically placed, one above 
the other. 

The voltaic arc may be produced between two elec- 
trodes of metal, but it differs from that between carbon 

228 



ELECTRICAL ENGINEERING 229 

terminals by a greater length for the same expenditure of 
energy, by its flaming character, and by a coloring due to 
the metal employed. 

173. With a pressuic of about 45 volts an arc can be 
produced between two pieces of prepared carbon, if they 
are first pressed together. The current, finding considerable 
resistance, heats the touching points to a white heat, hardly 
visible, however, because each point serves as a screen 
for the other. On separating the carbons, volatilization of 
the carbon takes place, filling the air space with a large 
quantity of incandescent carbon particles, offering so slight 
a resistance, that a comparatively low pressure will main- 
tain the current. The positive carbon grows much hotter, 
gives off much more material and is therefore consumed 
more rapidly than the negative one, in the case of a 
direct current ; it is hollowed out, while the negative carbon 
shows a sharp point. In the case of an alternating current 
both carbons show the same shape, slightly hollowed out, 
and they are consumed at equal rates. 

Temperature and brilliancy 

174. In this hollow or "crater" about 80 per cent of the 
total heat and light are generated, about 10 per cent in 
the negative carbon, and about 5 per cent in the incan- 
descent air space. The temperature of the positive crater 
is estimated at 3500 — 4000° C, that of the negative point 
at 2250 — 3000° C. The brilliancy of carbon at this heat 
is 8000 times greater than that of platinum at 775° C. 
Liquid carbon has not been seen by any human eye. It 
seems that carbon at about 3500° C changes from the. 
solid state through the liquid to the gaseous state. The 



230 MODERN ELECTRICITY 

globules seen on the carbon ends are due to melted silica 
or other impurities in the material. 

175. The voltaic arc is the source of the most intense 
heat and brightest light which man can produce. This is 
due to an intense localization of both resistance and heating 
effect. The concentration of heat is favored by the poor 
thermal conductivity of carbon. The localization of resistance 
is aided by a thermo-electric effect consisting in a counter- 
electromotive force caused by the enormous difference of 
temperature in the two pencils. 

The light of the arc most nearly approaches sunlight in 
color ; it looks yellowish during the daytime ; its blue or 
violet color at night is only apparent, and due to optical 
illusion. The human eye, being accustomed to the yellow 
artificial light of kerosene or gas lamps, and therefore 
unconsciously comparing the arc light with them, ascribes 
to it bluish tints. 

Pressure 

176. Of the 45 volts mentioned on page 229, about 39 
are spent at the surface of the crater ; the remaining volts 
maintain the arc. Consequently a potential difference of at 
least 39 volts is required for each arc lamp to set up 
volatilization, and generally about 50 volts are required to 
secure a steady light. At that pressure the proper distance 
for the two carbons from each other is about 3 millimeters. 

When the distance is excessive, the negative carbon 
becomes blunt, and the arc flickers considerably, moving 
from one side to the other When not far enough apart 
the negative carbon tapers too much, the crater is formed 



ELECTRICAL ENGINEERING 231 

imperfectly, and is screened too much by the negative carbon. 
reducing the illuminating power considerably. 

Candle power 

i77. Reccrds show that usually one horse-power is used 
for an ordinary 875 candle-power lamp using 10 amperes 
under a pressure of 50 volts. The remaining 246 watts 
(746—500) are lost in the various conversions, and from 
other causes described in preceding chapters. Such a lamp 
is usually spoken of as a 2000 nominal candle power lamp. 
Those used with 6-5 and 4 amperes are called 1200 and 
600 nominal candle-power lamps. A "candle-power" equals 
the light given off by a spermaceti or paraffine candle of 
a fixed quality, size and form, varying in different countries. 
The British standard candle is a spermaceti candle seven- 
eights of an inch in diameter, weighing one-sixth pound, and 
burning at the rate of 120 grains per hour. 

Because the crater is the part that gives the most 
light, the positive carbon is generally placed on top, so as 
to throw the greatest amount of the light downward. For 
this reason, also, the direct current is prefered to the alter- 
nating, and the negative carbon is generally a little thinner 
than the positive one, in order to screen the light as little 
as possible. For each type of lamp a candle power curve 
is established, showing the amount of light it will shed in 
various directions. See fig. 97. Globes of clear glass 
reduce the light by about 10 per cent., ground glass from 
30 to 50 per cent. 

The carbon 

178. The carbons, in order to be perfect, must be very 
dense, uniform in structure, pure, and of low electrical resis- 



232 



MODERN ELECTRICITY 




Fig. 97. 



tance (from 0-15 to 175 ohm per foot). They are made 

of graphite mixed with pure carbon derived from the 

destructive distillation of 
gas-tar, bitumen, pitch 
or similar substances. 
After being ground and 
made into a paste with 
a syrup, rods are formed 
from ^\ to f inches in 
thickness, and baked 
several times. Finally, 
a copper coating is put 
on by electroplating. 
The positive carbon is 
usually 12 inches long 

and has a core, which serves to keep the crater central. 

The negative carbons are 7 inches long. 

The lamps 

179. Owing to the volatilization, previously described, and 
owing to some combustion, that is chemical union with the 
oxygen of the surrounding air, a mechanism is necessary 
which will press the carbons together at first, then separate 
them to a distance, strike the arc, in accordance with the 
amount of E. M. F. furnished, and finally feed the carbons 
together at a rate in proportion to their consumption. 
These several operations must be brought about electrically. 
In the most simple construction the action of striking the 
arc is controlled by the main or series coil, while the 
feeding is worked by a shunt coil. A lamp having both 
these coils is called differential. The coils must be perfectly 



ELECTRICAL ENGINEERING 233 

adjusted so as to operate automatically as the effect of 
one preponderates over that of the other. In other lamp 
types a clock work, or a most ingenious combination of 
electrical and mechanical devices, regulates the operations. 
The lower carbon is generally fixed, and the upper one 
is controlled by the mechanism. 

For some purposes, as for lighthouse or lantern work, it 
is necessary that the arc remains stationary, and both carbons 
must automatically move toward each other at their exact 
rates of consumption. The mechanism of such a focussing 
lamp is, of course, more complicated and expensive. 

In a double carbon lamp there are two sets of carbons, 
one of which has its circuit completed only after the other 
pair have been so far consumed that they cannot meet any 
longer, even when the current is stopped. Other types have 
fixed parallel or nearly parallel carbons termed candles, 
some of which burn across a thin wall of some insulating 
material, that is destroyed at the same rate as the carbon 
pencils. Such lamps need little or no regulating mechanism, 
but have other disadvantages that make them objectionable. 

A glass globe almost entirely tight by excluding nearly 
all air, causes a carbon to last from 65 to 150 hours, and 
the light is steadier ; but the globe must not be hermeti- 
cally sealed or it will explode. A vent must be provided 
for the excess of gas developed. 

Regulating mechanism 

180. Fig. 98 is a diagram illustrating a well-known form 
of regulating mechanism for a lamp designed for connection in 
series on a constant-current circuit. This type of lamp is 
much used for outdoor lighting. It has two electromagnets 




THE ELECTRIC ARC. 

(From photograph taken through smoked glass.) 

Showing the positive carbon with its crater, and the lower 

negative carbon with its point. 



234 



ELECTRICAL ENGINEERING 



235 




CLvrc* 



— 2>/tJ//-Pffr 



controlling the feeding of the carbons. One magnet is wound 
with coarse wire and is connected in series with the arc, and 

the other magnet is 
wound with fine wire 
and connected in a 
shunt or by-path around 
the arc. The series 
magnet lifts the upper 
carbon to start the arc 
when current is first 
turned on, and its ar- 
mature stays drawn down, as shown, 
during the entire operation. The shunt 
magnet regulates the feeding of the 
carbon ; its armature being connected 
with the clutch through the balanced 
lever mechanism in such a way that 
as the power of the shunt magnet 
increases, the clutch and carbon will 
be lowered. In the operation of this 
lamp, as the carbons burn away and 
the resistance of the arc becomes 
greater, the current through the shunt magnet increases, caus- 
ing it to feed down the carbon and keep the arc at the proper 
length. As the length of the arc decreases, its resistance 
decreases and the shunt magnet receives less current, so that 
the feeding is checked. When the clutch drops far enough 
to strike the plate immediately under it, it is loosened and 
allows the carbon rod to slip through. But as the arc is 
shortened, the shunt magnet is instantly weakened and the 




236 



MODERN ELECTRICITY 



clutch lifted by the spring which is connected to the lever 
mechanism, so that the proper length of arc is thus main- 
tained at all times. 

Another form of arc 
lamp, shown in fig. 99, 
has a much simpler 
mechanism, requiring 
but a single electro- 
magnet, which is in 
series with the arc. 
Such lamps as this 
must be connected in 
multiple arc across the 
mains of the system, 
the potential' being con- 
stant while the current J= 
through each lamp may 
vary according to its 
resistance. As the arc 
becomes longer, the in- 
creased resistance cuts 
down th e current 
through the magnet, 
which, becoming weak- 
ened, feeds down the 
carbon to maintain the 
proper length of arc. 
This is called a con- 
stant-potential lamp, 
and in lamps of this FlG> 99 . 




ELECTRICAL ENGINEERING 237 

kind the arc is usually enclosed within a small glass globe 
which is nearly air-tight. The advantage of enclosing the arc 
is that the absence of fresh air — oxygen — prevents the carbons 
from burning away as fast as they otherwise would. If the arc 
is not enclosed the carbons of an ordinary lamp will be con- 
sumed in about eight hours, while an enclosed arc lamp 
will burn about 150 hours before new carbons are required. 
The enclosed arc, while steadier and more silent than the 
open arc, does not give so bright a light, and the light has 
more of a violet tinge. Enclosed arc lamps are at present 
generally constructed for connection in parallel on constant- 
potential circuits, such as incandescent lighting circuits, so 
that both arc and incandescent lamps may be used for indoor 
lighting on the same circuit. When the arc is enclosed the 
carbons burn flat at the ends as shown in fig. 99, since the 
crater formed wanders slowly over the surface of the positive 
electrode, leaving the ends fairly flat. 

The circuit 

181. On a constant current circuit, arc lamps may be used 
in series, and on a constant pressure circuit automatic cut-outs 
are often provided, especially on long lines, which open another 
path, of low resistance, in case the main circuit through a 
lamp is from any cause interrupted. 

Where a number of series arc-light circuits are supplied 
from one station, an arrangement is needed by which any 
generator may supply any circuit. Generally there is a switch- 
board with a spring jack for every main wire, and a cord and 
plug for every dynamo. 

Incandescent lamps 

182. The first incandescent lamp, consisting of a thin 
stick of carbon brought to white heat in a vacuum, 



238 MODERN ELECTRICITY 

was made as early as 1845, but the difficulties in the way 
of making it a commercial success were so many that 
almost 35 years more passed, before Edison in America, 
and Swan and others in Europe succeeded in devising a 
substance that gave a brilliant light and could be produced at 
a reasonable price. 

The principle 

183. In §60 the I 2 R loss has been explained. The 
heat into which a part of the electrical energy is always 
converted in a conductor, was at an early period expected 
to furnish a new light, but no metal could be found that 
would not be dangerously near the melting point when incan- 
descent, with the only exception of iridium which is too 
expensive to come under consideration in this respect. 
Moreover, the resistance of metals increases with rising tem- 
perature, while the resistance of carbon decreases. Carbon 
cannot be melted by any ordinary means and for these 
two reasons is especially fitted for the purpose ; but it 
oxidizes readily when heated, and the great difficulty has 
been to exclude the free oxygen of the air from the bulb in a 
manner that was at once efficient and economical. The 
temperature developed in the incandescent filament is about 
2000° C 

The filament 

184. The filaments may be divided into two classes: 
first, those in which the original fibrous structure of the 
carbonaceous body is retained, as in the Edison filament, 
made of a kind of bamboo or of cotton thread ; and second, 
those in which it is intentionally destroyed, the material 
being worked into a homogenous viscid mass, cellulose, 



ELECTRICAL ENGINEERING 239 

and shaped by being squirted through a fine aperture, as in 
the filaments of Swan and other inventors. 

The material is first carbonized in a solution of two parts 
of sulphuric acid to one part of water, then the acid is 
washed out in running water and the material is dried. It is 
then in a horny, transparent state. Often passing through a 
series of jewel dies which reduce it to a uniform gauge, 
it is wound on a frame, that is arranged to give the filaments 
the shape desired, with or without loops. A number of these 
frames are placed in a crucible and the empty spaces filled 
with powdered charcoal. The crucible is then sealed air- 
tight and brought to a white heat in a furnace. The char- 
coal absorbs any oxygen in the crucible, that would otherwise 
destroy the filaments The high temperature has the double 
effect of rendering the filament hard and durable, and also 
less porous so that it will not be liable to occlude (absorb) 
gases, which when heated would expand and cause minute 
fissures in the carbon. Then the filaments are cut to the 
desired length, fastened in pairs of clips connected with 
electric terminals, and immersed in coal gas or naphtha 
gas. Flashes of current sent through the filament heat the 
thinner parts more than the others, in consequence of which 
the carbon of the gas is deposited on the filament in pro- 
portion to the heat. The flashing is continued, until the 
filament shows a uniform luminosity. 

The filament, when finished, is mounted on two short pieces 
of exceedingly thin platinum wire, which are sealed in a bit of 
glass. The ends of the wire, flattened, are bent around the fila- 
ment and fixed with a carbonaceous cement, or in some other 
way. Though more expensive than gold, platinum is the only 




240 MODERN ELECTRICITY 

metal suitable for the purpose, because it happens to expand 
or contract with the varying temperature at almost exactly the 
same rate as glass. This glass is then sealed into the glass of 
the bulb. The metallic filament lamps are being used quite 
extensively in the last few years, even replac- 
ing arc lights and carbon filament lamps to 
a marked degree. Their cost is slightiy 
greater than the carbon filament lamps but 
the increase in light and the decrease in 
power consumption offsets this. The metal filaments 
are made of fine tungsten or tantalum wire. The 
construction of the lamp is similar to the carbon 
lamp with the exception of a much firmer and much 
longer filament. 

The vacuum 

185. The bulb to be exhausted is provided with a 
short glass tube by means of which it can be con- 
nected to an air pump. The vacuum is created by 
any one of several forms of mercury pump. Fig. 100 
fig. 100. illustrates the principle of the Sprengel pump, which 
may be considered typical. It consists of a barometer glass 
tube about 40 inches long, with a branch C, connected with the 
lamps L to be exhausted. The reservoir A is partly filled with 
mercury and so connected with the tube that the pinch-cock 
allows the metal to drop in small drops only. Each drop forms 
a piston and in rushing past the junction C carries before it a 
little air from the branch and lamps L. The diagram shows 
the minute quantities of air between the drops of mercury all 
the way down to the lower flask into which the mercury des- 
cends as fast as the column in the vertical tube tends to grow 
longer than 30 inches. When the air spaces between the 
mercury drops disappear, the bulb is exhausted and may be 



ELECTRICAL ENGINEERING 241 

sealed off by fusing the small connecting tube D and drawing 
it out to a thread. 

Base and socket 

186. The exhausted bulb is next mounted in a brass collar 
or base fixed with cement, in which two free platinum wire ends 
are connected with two brass segments insulated from one 
another, The collar again fits into a holder or socket, in 
which the electrical contact is brought about in many different 
ways. In some types the base is screwed into the socket, 
contact taking place as soon as it is screwed in far enough. 
Some types have a switch in the socket, but they get out of 
order easily, which is natural when the smallness of the parts 
is considered, and the high temperature when the lamp is burn- 
ing. Better have independent switches in convenient places. 

Life of a lamp 

187. The time the filament of an incandescent lamp will 
ast varies considerably. It depends greatly on the quality of 
the filament and the degree of vacuum in the bulb, also upon 
the strength of the current. Experience teaches that a fila- 
ment is not injured by a current strong enough to bring out its 
full luminosity, but a lamp will last longer if a comparatively 
feeble current is used. To insure a steady light, the pressure 
at the terminals of the lamps must be perfectly constant, 
because a slight variation in the pressure will cause a large 
variation in the luminosity. A 16-candle power lamp requiring 
a pressure of 110 volts, for instance, will give only 12-candle 
power at 105 volts, while at 115 volts it would show great 
brilliancy but burn out very rapidly, and the power consumed is 
considerably increased ; the decrease in the life of the lamp is 
at a far more rapid rate than the increase of the voltage. 

The efficiency of a lamp is generally expressed by the 
ratio or candle power yielded to watts absorbed. A new lamp 



242 



MODERN ELECTRICITY 






3-A 


4-A 


9 


e-cp. 


16-C.P. 


Fig. 


101. 





usually has an efficiency of 1 -s- 3-5 =0-2857, but it deteri- 
orates very soon, and it is a good lamp that then shows 
the ratio 1 -5-3*75. The continued efficiency of a lamp is 

of much more im- 
portance than a 
long life, and exper- 
iments have proved 
that the life of a 
lamp increases 
much more rapidly, 
than its efficiency 
decreases. 

If a lamp that 
takes 2-5 watts per candle lasts for 150 hours, one that 
absorbs 3*0 w. p. c. will last 350 hours, one of 3*5 w. p. c. 
lives 700 hours, and. one of 4*0 w. p. c. 1000 hours. 

Fig. 101 shows four incandescent lamps, together 
with the appearance of the filament from the point, 
and with the luminosity in different directions, 
expressed in candle powers. 

Fig. 102 illustrates the new " Economical " lamp. 
By a turn of the bulb either the small fila- 
ment with 1 c. p. or the large one with 16 
c. p. may be turned on. Fig. 103 represents the 
same lamp arranged so that a pull of one or two 
fig. 103. corc ^ s w ^ switch in one filament or the other. 

Rating of lamps 

188. After the lamps have been perfectly mounted they 
are tested with regard to candle power, pressure and cur- 
rent and slips of paper showing the illuminating power. 





Fig. 102. 



ELECTRICAL ENGINEERING 243 

pressure and watt consumption are pasted on the bulb. 
There are many different rated lamps in the market ranging 
from 1 to 150 candle power. Usually 16 c. p. lamps requiring 
from 50 to 60 watts are employed. 110 volts, 55 watt and 
16 c. p. lamps require a current of 05 ampere. Lamps are 
usually made for 50, 60, 110 and 220 volts pressure. 

Incandescent lamps may be used for both direct and alter- 
nate currents. For example, when supplied with 50 volts 
direct current, a lamp will have the same illuminating power 
as when supplied with 50 volts alternate current. 

Connections for lamps 

189. Incandescent lamps may be operated upon series or 
parallel circuits, but the latter have been found to give 
more satisfaction. 

When connected in series, it is impossible to cut out of 
circuit one of the lamps, as by this operation the current 
is cut off from all the lamps of the circuit. If it is desired 
to cut off a lamp in a series circuit, the lamp must be short 
circuited, and special switches have been introduced in the 
market for this operation. When connected in a parallel 
circuit every lamp is entirely independent of the current 
flowing through other lamps of the same circuit, the current 
flowing through it depending only upon the resistance of the 
lamp and the pressure at its terminals. Any lamp of a 
parallel circuit may be cut out of circuit by a simple 
operation of the switch in the socket of the lamp and 
without interfering with the other lamps. (See § 155). 

Drop in mains 

190. When lamps are connected to long mains leading 
from the central station there is always a loss of pressure 



244 



MODERN ELECTRICITY 



in the mains, called the "drop," equalling the product of the 
current and the resistance of the wire. (See § 58). 

It is not advisable to allow the drop Jo be greater than 
twenty per cent of the dynamo pressure when all lamps are 
turned on, as it is very difficult to regulate the pressure of the 
dynamo when the drop is too great. For this reason, and also 
to save the cost of copper in mains it is advisable to transmit 
the current at a very high voltage and to reduce the voltage to 
the necessary value at the center of distribution. This may 
be accomplished by using an alternate current and transform- 
ers or rotary converters as described in § 128 and 141, 



Mercury vapor lamp 

191. The mercury vapor lamp (see fig. 104), consists of a 
long glass tube (a) about an inch in diameter. Mercury is 
placed in an expansion (b) at the lower end of the 
tube, from which the air has been partly exhausted. 
Two platinum terminals (c x c 2 ) are sealed into 
the tube, one on each end of it. The lamp may 
be operated on a 110 or 115-volt circuit, and an 
induction coil is provided to start the lamp by sup- 
plying it temporarily with high voltage current. 
This current instantly vaporizes a part of the mer- 
cury and the whole tube becomes filled with mer- 
cury vapors. These are brought to incandescence 
by the current passing through them, thus produc- 
ing light of a pale blue-green tint. The light con- 
tains no red rays, and casts no sharp shadows. 
fig. 104. It is very favorable for the eyes, causing but little 
fatigue, and has been used in draughting rooms to a great 
extent. It is also used for photographic work and for making 
blue prints. The efficiency of this lamp is about five times 





ELECTRICAL ENGINEERING 245 

that of ordinary incandescent lamps, being from 0*5 to 0-25 
watt per c. p. As there is nothing in the lamp which 
could wear, the lamp theoretically is everlasting and shows 
after a use of 2000 hours but slight decrease in efficiency. 
The mercury vapor lamp was invented by Peter Cooper 
Hewitt and first exhibited in April, 1901. 

Measurements of illuminating power 

192. Illuminating power of lamps is measured by special 
apparatus called photometers. The simplest apparatus is the 
original Bunsen photo- 
meter (named after its 
inventor) shown in dia- 
gram in fig. 105. A 
standard candle described 
in § 177 is placed in A. 

The electric lamp whose candle power is to be measured 
in B. C is a movable stand with two screens made of thin 
transparent paper on which grease stars a x a 2 have been 
drawn and placed at a sharp angle to each other. D is a long 
scale. When in use this photometer is usually enclosed 
in a perfectly dark room and the light of the candle A 
and the lamp B so screened as to fall on the grease stars 
a x and a 2 only. Then the screen C is moved on the scale 
until both of the grease stars a x and a 2 are equally illu- 
minated. When both stars are equally illuminated then 
the candle power of the candle A and lamp B are related 
to each other in ratio of the squares of the distances meas- 
ured from the screen to the candle and lamp respectively, 
because the light varies inversely as the square of the 
distance. 



Fig. 105. 



246 MODERN ELECTRICITY 

The candle foot 

193. The intensity of illumination of a surface by a lamp 
fixed above it is inversely proportional to the square of the 
distance from the lamp to the illuminated surface. The 
unit for measuring illumination of lamps is the intensity 
of illumination which a lamp of one candle gives to a per- 
pendicular surface placed at a distance of one foot. This 
illumination is called a candle foot. 

RULE 45. — The illumination produced on a perpendi- 
cular surface by a lamp equals the candle power of the 
lamp divided by the square of the distance from the lamp to 
the surface. 

Thus a 16 c. p. incandescent lamp being placed 4 feet 
from a sheet of cardboard gives it an illumination of 

— ? = — = 1 candle foot. 
4 2 16 

The illumination for reading should be not less than 2 

or 3 candle feet and the light should be placed so as not 

to meet the eyes. The average illumination of light rooms 

by daylight is about 35 candle feet. 

EXAMPLE 70. 

10 16 c. p. incandescent lamps are placed above a writing 
desk at a distance of 4 feet. What, is the illumination of 
the desk ? 

Total c. p. of lamps = 1 X 16 = 160. 

160 160. ,. . 

—r - = -rr=\0 candle feet. Ans. 

4 2 16 



ELECTRICAL ENGINEERING 247 

Questions and Answers. 

Q. What size of copper feeders is required for ten 110 
volt and 55 watt lamps connected in parallel, their center of 
distribution being 100 feet from a dynamo, generating 115 
volts. Pressure at center of distribution 1 1 1 volts. 

A. Current for one lamp = — - = 0-5 ampere. 

Current to be transmitted to center of distribution = 10 X 
5 = 5 ampere. 

Drop in mains = 115 — 111=4 volts. 
1079 X 100 X 2 X 5 



Circular mils = 



10,790 

■= 2697-5 c. m. Ans. 



4 

Q. A current of 8*5 amperes flows through an arc lamp 
where the fall of potential is 50-5 volts. How many watts 
are expended in the lamp? How many H. P.? 

A. Watts expended = 8-5 (amp.) X 50-5 (volts) = 429*25. 

429-25 
H. P. expended = = 0-58 H. P. (approx.). 

Q. How many watts are lost in heat in the preceding 
example when only 12 per cent, of the energy supplied 
appears as light? 

A. 88 per cent, of 429.25 is lost in heat. 

429-25 

— ^qq-X 88 = 377.74 watts. 



CHAPTER XIII. — The Telegraph and Telephone. 



The telegraph 

194. The earliest experiments with transmitting signals 
through wires were made as long ago as 1774 by Lesage 
in Geneva, who invented a system of transmitting mes- 
sages, which were read by observing the divergence of two 
pith-balls at one end of a wire, when a charge of electricity 
was sent into the other end. Many other inventors have 
worked on the problems of telegraphy, especially Ampere, 
(1821) Crooke and Wheatstone (1837) until Morse (1837) 
succeeded in constructing a telegraph system in which by 
the attraction of an armature by an electro-magnet marks 
were made upon a moving strip of paper. In 1844, his experi- 

j mental line connected 
the city of Washington 
with Baltimore. In 1845 
this line was opened to 
public traffic and after a 
year of successful opera- 
tion, the construction of 
Morse's system of tele- 
graph lines was under- 
taken in almost all parts 
fig. 106. of the civilized world. 

The Morse telegraph system contains the following parts : 

1. The Key. 3. The Line. 

2. The Battery. 4. The Morse instrument. 

248 




ELECTRICAL ENGINEERING 



249 



The Morse instrument 

195. The sounder or the Morse (see fig. 106), named 
after its inventor, is the most widely used apparatus in tele- 
graphy. It consists of an electromagnet a which when mag- 
netized by a current passing through its coils for a short 
length of time, attracts an armature screwed on lever b, 
a spring drawing the lever and the armature into their 
previous position when the current is stopped; at this time the 
lever b makes a click when striking against screw d\ another 
click is heard when the armature is attracted and when it 
strikes the screw c. This apparatus may be arranged to serve 
either as a sounder or as an embosser or an ink-writer. 



B 



THE MORSE ALPHABET. 
C D E F G H 



K L 

U V 



M N O 
W X 



P 
Y 



Q 

z 



R 

& 



S T 
1 



8 



9 



Comma (,) Semicolon (;) Colon (:) 



Colon Dash (: — ) Hyphen (-) Period (.) Interrogation (?) 

Exclamation (!) Dash ( ) Capitalized letter Paragraph (1J) 

Dollars ($) cents (c) Pound Sterling (£) 

Fig. 107. 

When used as a sounder it gives the operator the telegraphed 
letters in a special Morse-alphabet, composed of dots and 



250 MODERN ELECTRICITY 

dashes. (See fig. 107.) At each attraction of the armature, 
two clicks are heard, and the operator knows that a dot 
is signalled when the two clicks follow immediately after 
one another; when a dash is signalled the interval between 
the two clicks is longer. 

When used as an embosser, it is arranged so as to print 
dots and dashes on a strip of paper, which by means of 
an ordinary clockwork is drawn under the needle of the 
instrument. The ink-writer pushes a little wheel against 
the paper when its armature is attracted by the electro- 
magnet. 

The key 

196. The key (fig. 108) consists of a lever 
a which being pivoted may move up and 
down through a small range and strike a 
contact b when the button on one end of 

Fig. 108. 

the lever is pressed down by the opera- 
tor's hand. A small spring under the lever tends to push it 
to the upper end of its stroke when the operator's finger 
ceases to press the button down. 

When the key is in a circuit, the current enters it 
at the binding post, passes through the legs and the pivot 
into the lever, and when the lever is depressed and thus 
a connection with the other binding post at b is established, 
the current leaves the key to pass into the line. Thus circuit 
may be made or broken at will by depressing or raising the 
lever a. 

When the key is not in use, the circuit is kept closed 
by a switch lever c mounted upon the same base plate as 
the key, and adapted to wedge in under a flat contact spring 




ELECTRICAL ENGINEERING 



251 



the lower contact point and 



f -1 



d mounted at the side of 
electrically connected with it. 

When it is desired to 
transmit a message, the 
circuit is opened by press- 
ing the lever to one side 5 
and the key is manipulated 5 
at intervals necessary to 
transmit the signs of the Morse alphabet. 

The recording register 

197. The recording register consists of a 
clockwork, which being enclosed in a case, is 
so arranged as to draw slowly, a long strip of 
paper between its rollers and under an electro- 
magnetic writing apparatus, a long lever or 
marker of which, is moved by the armature of 
the receiving electromagnet. The sharp point 
or the writing wheel is held 
down upon the moving 
strip of paper as long as 
the circuit in the apparatus 
is closed and its magnets 
excited. When the circuit 
is broken the marker is 
lifted off the paper. Thus 
dots are printed when the 
circuit is closed for a mo- 
ment only, and dashes 
when the circuit is closed 
for a short length of time Fig. 109. 





252 MODERN ELECTRICITY 

so as to allow the rollers to move the paper unaer the point 
of the marker. 

The recording register is shown in fig. 109 which repre- 
sents a Morse transmitting station, receiving station and line. 

The telegraph line 

198. The current used in the telegraphic transmission 
of messages — its average being about forty milliamperes — 
allows the use of the earth for one part of the circuit 
(see fig. 109). The other part of the circuit consists ordi- 
narily of a galvanized iron wire supported on wooden poles 
and insulated from them by glass or porcelain insulators. 
Wires for telegraph lines are usually No. 8 to No. 6 B. 
W. G., but the size of the wire is often increased according 
to the length and the importance of the lines in order to 
prevent frequent faults in them caused by snow, wind, etc. 

The relay 

199. The relay or repeater is an instrument which is 
frequently used in working over long lines, where there are 
a number of instruments on a common circuit and when 
the current is- not strong enough to operate the recording 
register. 

The relay, a diagram of which is shown in fig. 110, con- 
sists of an electromagnet a having a lightly pivoted arma- 
ture b, the movement of which is controlled by a little spring c 
which, when attracted, closes the local circuit, consisting of 
battery d and the recording register e. 

The armature of the relay always works regardless of 
which direction the current flows and by placing many 
turns of fine wire on their magnet coils, relays are made 



ELECTRICAL ENGINEERING 



253 



so sensitive as to be operated satisfactorily with currents 
even smaller than 10 milliamperes. 




Fig. 110. 

Open and closed circuits 

200. The so-called open circuit working means the bat- 
tery is out of circuit when the line is in rest. The open 
circuit working is used on almost all European lines and 
has the advantage of not using the battery when messages 
are not being sent. 

In the closed circuit working, used among American 
telegraph companies, the current continues to flow through 
the line when messages are not being sent, but it is inter- 
rupted by the key of the operator when sending signals. 

This system allows the connection of a number of iso- 
lated stations on a single circuit, each of which can com- 
municate with all the others by opening the circuit. A 
further advantage of this system is that every failure in the 
line announces itself by stopping the current. 

Faults in lines 

201. The faults occurring most frequently in telegraph lines, 
are caused by one of the following reasons : either the insula- 
tor breaks and causes a short circuit, allowing the current to 



254 



MODERN ELECTRICITY 



pass to the earth before reaching the receiving station, or 
the wire itself breaks and falling on the ground establishes 
a short circuit. Insulation faults in stations are also fre- 
quently the cause of short circuits. 

Multiplex telegraphy 

202. For reasons of economy, in long and expensive lines, 
special arrangements have been made which allow the sending 
of more than one message from one station to another. If it 
is possible to send two messages at one time from one end 
of the line to the other, the line is said to be diplexed. If one 
message may be sent from each end at the same time, the 
line is said to be duplexed. When four messages may be 
sent at once, two in each direction, the line is said to be 
quadruplexed. The last system is a combination of the two 
preceding ones. 




Duplex telegraphy 

203. The commonly used method of duplex working is the 
so-called bridge-method. The diagram in fig. 1 1 1 shows a 
duplex station working with the bridge method. 

T',o circuit divides at a (a 1 ) into two branches, one of 
v.'hich :crnects at b (b l ) to the line, the other through a resist- 



ELECTRICAL ENGINEERING 



255 



ance c (c 1 ) to earth. When the ratio between the resistances 
in the sections of the circuit a b and a d equals the ratio 
of the resistances of the line and of c, then no current may 
pass through e (compare § 92) and e does not indicate any 
currents sent from a, but e 1 will show it, for the current pass- 
ing through the line and arriving at b 1 will divide into the two 
branches b 1 a 1 flowing over c 1 to earth and the other part 
flowing over b 1 e l d 1 and signalling in the apparatus e 1 . Even 
when the operator at the other end depresses the key /*, the 
apparatus e 1 will not cease to give signals, and the apparatus 
e will give signals even when the current in the line is 
stopped by an equal current sent from the opposite direction, 
because the current from a b will then flow through e as 
if it had been sent from the other station. 

Polarized relay h&l ra 

204. A relay possess- 
ing a permanently mag- 
netized steel armature is 
called a polarized relay, 
(see fig. 112). When 
there is no current pass- 
ing through the coils of 
the electromagnet, the 
magnetized armature will 
stand between the poles of the electromagnet, being restrained 
by two springs. When a current flows in one direction the 
armature will be attracted by one pole ; and when the poles 
of the electromagnet are reversed by a current flowing in 
another direction it will move to the other pole. It is possible 
to send a current toward a non-polarized relay, over the line 



<^*j 




Fig. 112. 



256 MODERN ELECTRICITY 

which is used for a polarized relay, without interfering with 
the working of the latter. 

Diplex telegraphy 

205. In this method, it is necessary to employ one set of 
instruments which only work with a current sent in one 
direction, and another set which works when a current 
sent in any direction exceeds a certain strength ; there- 
fore, polarized relays (see § 204) which respond only to 
currents in one direction, and adjusted non-polarized relays 
which respond to currents above a fixed minimum are used. 
There are two keys : one reversing the current for any 
direction and another which is so adjusted as to send 
weak or strong currents in one direction only. Two currents 
are used in diplex telegraphy. One being quite weak, is 
reversed when sending signals and thus operates a polarized 
relay. The other, a stronger current, is increased and de- 
creased when sending signals to work a non-polarized 
relay. The current is increased and decreased by a special 
key which alternately connects into the circuit a large and 
a small battery. 

Automatic and autographic telegraphy 

206. For sending quick messages such as stock quotations, 
press dispatches etc., machines are sometimes used instead 
of hand. The receiving stations then, consist of a machine 
receiver, which prints the messages in the English alphabet 
directly, and this operation is known as automatic telegraphy. 

Machines have been devised to transmit writings and 
sketches exactly as they were written or drawn. Most of 
these machines are very complicated and being too expen- 



ELECTRICAL ENGINEERING 25* 

sive and easily put out of order, are not in practical use. 
Machines reproducing writing are called autographic telegraphs.. 

Submarine cables 

207. Cyrus W. Field was the first man who entertained 
and financed the idea of laying a cable across the ocean. 
After several unsuccessful attempts, in 1858 he succeeded 
in laying a line from Newfoundland to Ireland. This cable- 
being too weak, was later replaced by another of a better 
construction, and the laying of it was completed in 1866 
when it was put into operation. Since then, a new cable has 
been laid almost every year, all forming at the present time 
a complete network, connecting in conjunction with the over- 
land telegraphs, almost all parts of the civilized world. 

Submarine cables are made with several separate con- 
ductors instead of only one, the different terminals of 
which, connect with different lines on the shore. The 
single conductors are made of three or seven copper wires, 
in order to do away with the easy breaking of the cabies 
The covering is of hemp or jute impregnated with tar, asphalt, 
or similar compound, spun around the insulated core to serve 
as a protection for the cable against the pressure of the iron 
wire, which forms the armor of the cable. 

Working on submarine cables 

208. The ordinary Morse telegraph is not suited for 
use in submarine telegraphy; therefore, a delicate instrument 
designed by Lord Kelvin is used. It formerly consisted of 
a galvanometer of very high resistance, having on its magnets 
a small mirror. At a -considerable distance and opposite to 
the galvanometer, a scale was placed at the center of which, 



258 MODERN ELECTRICITY 

was a smal 1 vertical slit. The rays of a lamp behind the slit, 
concentrated by a lens, were allowed to fall upon the mirror 
and reflect from it upon the scale. The dots and dashes 
of the Morse alphabet were indicated by the movement of the 
reflected spot, to right or left of the center of the scale. 

Later, Kelvin's syphon recorder was introduced and it has 
been constantly employed since then. It consists of a flat coil 
of very thin wire, which is in circuit with the line and 
is suspended on silk fibres between the poles of a powerful 
magnet. When there is a current passing through the 
coil, it tries to set itself with its plane, perpendicular to the 
line joining the poles of the electromagnet. The coil com- 
municates its motions to a very fine glass syphon, one end 
of which dips into a vessel of ink ; the other, when a current 
passes through the coil, draws a wavy line on a ribbon 
of paper, which is moved under it by clockwork. This 
wavy line is a perfect record of the message, in Morse 
alphabet ; its lines in one direction corresponding to the dots, 
and those in the other direction to the dashes. 

The telephone 

209. In 1861, Prof. Philip Reis of Friedrichsdorf, Ger- 
many, was the first scientist whose experiments with the 
telephone proved a success. In his imperfect instrument 
the sound waves were caused to act upon a point of loose 
contact in a circuit, and thus to vary the resistance of the 
circuit The simplest telephone transmitted music and speech, 
imperiectly though, owing to the lightness of the contact 
employed. Later inventions which made the telephone prac- 
tical, were those of Alexander Graham Bell (1876) and Dr. 
c-lisha Gray. 



ELECTRICAL ENGINEERING 259 

The first practical telephone constructed by Belf and 
exhibited at the Philadelphia Exposition in 1876 is shown 
in fig. 113. It consisted of two similiar apparatus, the 
transmitter being used to talk into and the receiver repro- 
ducing the sounds. Each of these two instruments consisted 
of a rod magnet m, around which, fine wire was wound and 
a Diaphragm or disk d, made of thin iron and placed in the 
field of the magnet. Each apparatus was provided with a 
special mouthpiece, of such a shape as to gather the largest 
possible amount of sound and concentrate it upon the 
diaphragm. There was no battery used in this circuit, the 
ends of the magnet coils being first connected with two 
wires, later with only one wire, while the two other ends 
were grounded as shown in fig. 113. 



m 



3 . LftfE 



-m 



t/7/tra 




Fig. 113. 

The working of this telephone may be explained in the 
following way: Many magnetic lines of force of the rod 
magnet m, pass the coil, and some of them enter the diaph- 
ragm d, pass through it and return toward the opposite pole. 
When the speaker's voice causes the diaphragm to vibrate, 
however slight the vibration may be, a larger amount of 
magnetic lines of force enters the diaphragm when it 



260 



MODERN ELECTRICITY 




Fig. 114. 



approaches the pole of the 
magnet, while less lines en- 
ter it when it moves away. 
Through this operation, the 
number of magnetic lines of 
force passing through the coil 
is decreased when the dia- 
phragm approaches the pole 
and increased when it moves 
away from it. When these 
changes occur in the number 
of magnetic lines of force, 
which pass through the coil, 
an electric pressure is set up 
in the coil, as explained in 
§ 80. The current flows in 
one direction, when the num- 
ber of magnetic lines of force 
passing through the coil in- 
creases, and in another direc- 
tion when it decreases. This 
faint current transmitted to 
the receiving appara- 
tus increases or de- 
creases the strength 
of its magnet, thus 
altering the amount of 
attraction the magnet 
exerts upon the dia- 
phragm d. The dia- 



ELECTRICAL ENGINEERING 



261 



phragm of the receiver is thus set into vibrations which cor- 
respond to those of the diaphragm of the transmitter and 
result in producing sound-waves like those which act upon 
the diaphragm of the transmitter. 

The receiver 

2io. Fig. 114 shows the improved receiver, which is now 
in general use. Like its old type, it consists of a permanent 
magnet equipped with a coil and a diaphragm made of thin 
varnished iron, which are en- 
closed in a hard-rubber case 
for protection from variations A 
of temperature, moisture, etc. 

There are various types of 
receivers on the market, most 
of them differing in shape only, 
and all combining the essential 
features of permanent magnets, 
bearing coils on their poles and 
a thin iron diaphragm destined 
to transform into sound-waves 
the impulses brought in current 
form along the line from the 
transmitter. 

The transmitter 

2n. The transmitter con- 
structed by Bell was not power- 
ful enough to transmit electrical 
impulses satisfactorily over long distances; a more powerful 
current was needed to overcome all obstacles in the line. 




Fig. 115. 



262 



MODERN ELECTRICITY 



Berliner, Hunning, Edison and Blake, have designed trans- 
mitters based on the theory of varying pressure, which 
transmit electrical impulses more effectively. Fig. 1 15 shows 
a section of the Blake transmitter. 

In this instrument the diaphragm a, surrounded by a 
rubber ring k, is fastened behind the aperture of the 
mouthpiece b. A short piece of platinum wire c, fixed to 
a fine spring d, touches the back of the diaphragm with 
one end, the other establishing a loose contact with the 
polished surface of a carbon button e, fastened to a spring 
/. The contact of the platinum wire and the carbon button 




may be adjusted by a screw h. Electrical impulses beating 
against the diaphragm, press to a greater or lesser degree 
the platinum wire c, against the carbon button e, thus varying 
the resistance of the contact. When this transmitter is con- 
nected into a circuit, the current of a battery passes through 
d, c, to e and / and then to the coil of a receiver. 



ELECTRICAL ENGINEERING 



263 



Being compelled to overcome a greater or a lesser resist- 
ance between c and e, the strength of the magnet of the 
receiver decreases or increases, thus producing the original 
sounds as described in § 209. 

There are many different systems of transmitters using 
granules (one of which is shown in the center of fig. 116) or 
small globes of carbon as a means for establishing and vary- 



ing the contact. The 
most widely known. 



Berliner and Ericson types are the 




Microphones 

212. A device for ren- 
dering faint or distant 
sounds distinctly audible, & 
is called a microphone. 
The principle of the mi- 
crophone is shown in fig. 
117. It consists of a 
stick of carbon <?, which 
being cut to sharp points 
on both ends, is held loosely, between two blocks of car- 
bon b and <:, which are fastened to a thin pine-wood 
board d. The microphone illustrated is in circuit with 
battery B and receiver R. When the board d, is also 
brought to vibration, thus establishing a more or less 
perfect contact of carbon stick a with the carbon blocks b and 
c, and offering the current passing through these contacts 
more or less resistance, the receiver R will reproduce the 
faintest sounds. Transmitters using microphones are called 
microphone transmitters. 



264 



MODERN ELECTRICITY 




The telephone induction coil 

213. In order to make the microphone transmitter, which 
may be operated usually with one or two battery cells, suitable 
for work over long lines, electromagnetic induction is used to 
strengthen the effect of the transmitter. For this purpose, 
especially designed induction coils are used in connection with 
the transmitters, the effect of which, is to do away with the 

scratching sound caused by the 
carbon particles of the transmitter. 
A section of such an induction 
coil is shown in fig. 118. The 
core a, of the induction coil, is 
made up of pieces of soft iron 
wire inserted into b, a tube of insulating material. The 
primary winding c, is of coarse wire, the secondary d, of 
thin wire as described in § 82. The primary coil is then 
connected in series with the transmitter and battery and 
the secondary coil in series with the line, as shown in 
fig. 116. 

The magneto=generator and the bell 

214. The magneto-generator consists of a number of 
permanent horseshoe magnets, which are so arranged that 
an armature mounted on a crank, can revolve between the 
magnet poles, thus producing an alternate current which is 
sent toward the bell, (see § 81.) 

The bell consists of a polarized magnet having two poles 
and an armature, which is pivoted in its center, so as to 
allow it to sway from side to side as it is alternately 
attracted by the magnet-poles. The current from the 
magneto-generator, being an alternate current, causes the 



ELECTRICAL ENGINEERING 



265 



armature to be attracted by each pole successively, the 
rod or clapper vibrating then with great rapidity and striking 
the two gongs above it one after another 

Complete subscriber sets 

215. A complete telephone set, two of which may be 
used for connecting two distant places, is shown in diagram 
in fig. 1 19. This set 

consists of a transmit- C/Xct f 

ter, induction coil, bat- 
tery, receiver, a bell and 
the magneto-generator. 

The telephone switch 
lever a, is pivoted at 
one end a f , the other 
end being formed into 
a hook to support the 
telephone receiver /, 
when not in use. This 
switch lever a, is provided with a spring which tends to hold it 
in its elevated position, and in which it touches the two con- 
tact springs c cK When the receiver is hung on the hook, its 
weight overcomes the tension of the spring, and the switch 
level touches a contact, thus completing the circuit from 
line 1 to a f through the polarized bell b, magneto-generator 
g to line 2. When the lever is in the position just described, 
the bell b, of this station will ring when the crank of the 
magneto-generator is turned on the other point. 

By lifting the receiver /, the lever a is brought into 
contact with the springs c and c f thus completing the two 
circuits: The one consisting of the microphone transmitter 




Fig. 119. 



266 MODERN ELECTRICITY 

V t local battery and primary windings p, of induction coil: 
The other of line /, secondary windings s, of induction coil 
receiver t t and line 2. 

The local battery is always cut out of circuit when the 
telephone is not in use and when the receiver rests on 
the hook. When a signalling current is sent from the 
other end of the line, the bell is rung ; and, in taking the 
receiver from its hook to answer the call, the circuits are 
automatically changed — the bell and the magneto-generator 
being cut out of circuit and the transmitter, local battery, 
receiver and induction coil brought into circuit. 

When it is desired to call up the other point of the 
line, the crank of the magneto-generator is turned while 
the receiver rests on the hook, and then the receiver is 
taken off the hook to listen for the answer of the station 
called. 

The bell is sometimes connected in parallel with the 
magneto-generator, or bridged. 

Central exchange 

216. In cities, the lines of all the users of telephones, 
are connected and lead into a common center known as 
the central exchange, and there to a switchboard, each line 
having its own number. The subscriber, when wanting tc 
speak to another, calls by means of his magneto-generator the 
central exchange, which connects him with the desired 
number, having signalled it with the magneto-generator. 

The telephone switchboard 

217. The switchboard is the means by which the tele- 
phone operator quickly connects the subscribers. As there 



ELECTRICAL ENGINEERING 



267 



is almost always a very large number of lines connecting 
with a common switchboard, they are generally very com- 
plicated. 

Fig. 120 shows a 
simple ten-line 
switchoard; As may 
be seen, the switch- 
board consists of two 
distinct parts, one the 
vertical board with a 
series of drop shut- 
ters or drops, and a 
series of round aper- 
tures lined with 
metal with an appara- 
tus jack (spring jack) 
behind the board, and 
a horizontal board 
upon which appear a 
row of upright instru- 
ments, the plugs, and 
sometimes a row o 
short levers. 




Fig. 120. 



The jack and plug 

218. The jack is an (see A fig. 121) arrangement, by 
means of which, the connection of two subscribers may be 
made, by inserting the plug B into its aperture, so that it 
comes into contact with the line by touching the spring a. 
The forward end of the spring a, rests in its normal position 
on a pin b, which being safely insulated from the base c t 



268 



MODERN ELECTRICITY 



connects with the wire leading through the coil of the drop 
to the ground. Normally, therefore, the line wire is connected 




Fig. 121. 

to the ground. When the plug is inserted into the aperture 
of the jack, it disconnects the line from the ground by 
lifting the spring a from the pin b and establishes a con- 
nection of the other line to the jack where another plug, 
connected with the former by a flexible cord d t is also 

inserted. 



^ 







\-c The drop 

219. The drop 
(see fig. 122) is 
an apparatus in- 
d tended to attract 
the attention of 
the operator 
when a subscrib- 
er wishes a con- 
nection. The electromagnet a, is mounted on the back 
of the switchboard's front plate , in which an aperture 



ELECTRICAL ENGINEERING 269 

has been left, to allow a rod b pivoted in c and con- 
nected with the armature d of the electromagnet, to move 
up about one quarter of an inch. The rod b, is provided 
on its forward end, with a hook which holds the drop 
shutter e in its raised position. When a current from 
the magneto-generator of a subscriber passes through the 
coil of the electromagnet a, the armature d is attracted, 
thus lifting the rod b. The drop shutter e y falls down (see 
dotted position of shutter) and displays to the operator the 
number attached at /, by which the line in designated. 

Operation of switchboards 

220. Fig. 123 shows a diagram of a grounded or com- 
mon-return switchboard. Keys a, b, c, are the operating keys, 
a and c, being the ringing keys, and b the listening key. The 
plugs e and d, connect by their flexible conducting cords 
with the ringing keys c and a respectively. Each of the keys 
has two contacts / and 2 which enable it to be in con- 
nection with either of two circuits. The switchboard shows 
the magneto-generator g, the operator's telephone set /, 
the drop k, jack j, and clear-out-drop /. When the sub- 
scriber whose line connects to jack /, desires a connection 
the current of his magneto-generator passes through line, 
through jack y, and coil of the drop k, to ground, thus 
releasing the shutter of the drop and exposing the number 
of the subscriber's line. The operator inserts plug e into 
the same numbered jack y, depressing at the same time 
the listening key b , thus connecting his own telephone 
set /, in circuit with line. By these operations, the operator 
is enabled to converse with the subscriber, the circuit being 
complete through the line wire, the jack j, the plug e, and 



270 



MODERN ELECTRICITY 



its cord, to contact / of key c and thence through spring of 
key b to the telephone set /, which contains a receiver, a 
transmitter, induction coil and 
battery, and ends in the 
ground connection, like all 
subscriber sets. When the 
subscriber has told the opera- 
tor the number with which he 
wishes to connect, the opera- 
tor inserts plug d into the 
jack of the desired number, 
depressing at the same time 




ELECTRICAL ENGINEERING 271 

the ringing key a, thus throwing into circuit his own magneto- 
generator g, whose handle he turns. Thus a circuit is 
established from the ground in the exchange, through the 
magneto-generator g, the contact 2 of key a, cord and plug 
rfand through the jack with the desired line, and subscriber's 
apparatus, the bell of which is rung. Then the two sub- 
scribers may converse, being connected across the clearing- 
out drop /', whose shutter falls, when the subscribers having 
finished their conversation "ring off" by means of their 
magneto-generators. Then the operators releases the plugs 
e and d, from the jacks of the two subscribers, the pulley 
weights /?! and h 2 bringing them back into the position shown 
in the cut. The grounded circuit switchboard has practically 
passed out of existence and, while a few of them may be in 
use, they are not manufactured at present. 

Common battery telephone system 

221. The various faults, formerly found in telephone lines, 
were generally caused by faults in the subscriber's battery 
or magneto-generator. 

The magneto-generator being the most expensive instru- 
ment in the subscriber's set, and easily put out of order, 
attemps were made as long ago as 1878 to do away with 
it, also dispensing with the battery ; and to supply the current 
necessary to transmit speech and to ring the bells from 
a common battery located at the central exchange. This 
system developed rapidly and at present is used in almost all 
large exchanges. / 

In the so-called central energy, or common battery system, 
the current is generated at the central exchange and sup- 
plied to storage batteries which, having an extremely low 



272 MODERN ELECTRICITY 

internal resistance and being able to maintain a constant 
E. M. F. for a considerable length of time, are well fitted 
for use in telephone work. From the secondary batteries, the 
current is sent over the switchboard to the subscribers. Thus 
the current of all subscribers is brought under control of the 
operator at the switchboard, the cost of frequent inspection of 
the subscriber's sets is greatly reduced, and the cost of repairs 
and renewals of batteries practically annihilated. 

Automatic telephone system 

222. The mistakes made by operators when connecting and 
disconnecting the lines of subscribers at the central exchange 
and the high cost of the operator's labor, induced many to 
consider the problem of operating central switchboards 
automatically ; in other words, to make it possible for every 
subscriber to establish and break the connection with the num- 
ber desired without the intervention of the central exchange. 
The earliest machines for this purpose were invented in 1879 
by Messrs. Connolly and McTighe, at Washington, D. C. 
Being very complicated and therefore not practical, these 
machines have never been used. In 1891 Strowger developed 
another machine which met with a similar fate, but Keith and 
Erickson finally improved the original Strowger machines and 
with these improvements they have been put into successful 
operation. To go into details of construction of the apparatus 
involved is beyond the scope of this book, therefore a mere 
mention is made in reference to the automatic telephone. 

In the automatic system the central switches are governed 
in their action by the subscriber who desires connection or 
disconnection as the case may be. The preliminary action 



ELECTRICAL ENGINEERING 273 

of calling for the number of the party sought is done by 
operating the dial on the telephone. In this way the sub- 
scriber makes his own connection with any one desired. In 
the same way the subscriber is able to disconnect himself 
from the line. 

Questions and Answers. 

Q. What is a pole-changer? 

A. A key for sending telegraphic signals by reversing the 
current. 

Q. What is a telegraphophone ? 

A. An apparatus which, by means of an electromagnet 
whose coils are in circuit with the subscriber's telephone 
set, registers spoken words on a moving strip of steel, so 
that they may be reproduced by means of a simple receiver, 
under whose magnets, the strip is moved. 

Q. A common telephone switchboard consists of what 
apparatus ? For what purpose do these apparatus serve ? 

A. The drops or lamps serving to attract the operator's atten- 
tion to the number of subscriber who wishes connection. 

Spring jacks and plugs, by means of which, connection, 
between two subscribers is established. 

Clear-out-drops, or lamps announcing to the operator that the 
subscribers have finished their conversation. 

Operating keys. The ringing keys being used to call sub- 
scribers by ringing the bells of their sets, the listening 
keys being used to bring the operator's set into circuit for 
communication and connection of the switchboard operator 
with the subscriber. 

Q. An operator's set consists of what apparatus? 

A. Of receiver, transmitter, battery and induction coil. 



CHAPTER XIV.— Wireless Telegraphy. 

Ether 

223. The earth is surrounded by air ; an atmosphere 
which is supposed to extend about twenty miles above 
its surface, forming a hollow ball, the smaller or inside 
diameter of which, is that of the earth, the larger or outer 
diameter equalling that of the earth, plus about forty 
miles. It is said that the distance between the earth 
and the sun is more than ninety million miles and it is 
generally accepted, that between the sun and the atmos- 
pheric globe described above, there exists some unknown 
substance, which scientists call the ether. It is supposed 
that the ether is a fluid medium existing in all space, 
permeating the denser atmosphere, passing through all sub- 
stances, gases, liquids, and solid bodies, just as light pene- 
trates a plate of transparent glass. Even the molecules 
of metals and minerals are not impervious to this invisible, 
ever present, mysterious, liquid substance. 

Waves 

224. Undulations of fluid or semi-fluid surfaces, commonly 
known as waves, are known and understood by everyone. 
When striking the smooth surface of a pond with a stone 
or stick, waves are set up, which rapidly transmit their 
motion to the remaining part of the surface of standing 
water, causing it to wave. Thus produced, they extend 
in all directions from the point of generation until they are 
broken by some object floating on the water or by the 

374 



ELECTRICAL ENGINEERING 



275 



banks, or if the pond be very large they become by friction 
smaller and less visible until they entirely disappear. 

Imagine fig. 124, were a section of the undulating sur- 
face of water, which, when in rest, is represented by the 
line M. The distance between the highest points of a wave 
A, is called its length. The distance B, between the high 
est and the lowest point of a wave is called its ampli- 
tude. The line M, which divides the amplitude B, into 
two equal parts is called the axis of the wave. 




Fig. 124. 

Interference of waves 

225. If two points of the surface of the water in a 
pond were struck simultaneously, the waves extending from 
these points, would meet with each other and break. This 
meeting and breaking is called the interference of waves. 
The wave length and amplitude depends upon the strength 
of the blow upon the surface of the water. 

When waves are set up, the particles of water are caused 
to vibrate along a line perpendicular to the surface, assum- 
ing their former position, when the waves subside. 

Transverse and longitudinal vibrations 

226. Fig, 125 represents a pulley A, over which, lies a 
thin wire B, one end of which, is connected to a circular 



276 



MODERN ELECTRICITY 



piece of wood C, (called a floater,) the other, to a weight 
D, which however high or low the floater C may swing, 
keeps the wire B, strained. By dropping the floater on the 
surface of water, M, waves are produced which cause the 
floater to swing up and down along a line perpendicular to 
the surface, N-O, which line in this example is represented 

by the strained wire B. 
The weight D, moving up 
or down will indicate pre- 
cisely the height of the 
waves set up. 

Such vibration described 
in the example above, 
where the particles swing 
perpendicular to the direc- 
tion of the waves, is called 
transverse vibration, and 
is represented in the above 
example by the swinging 
floater in its relation to 
the waves set up, by drop- 
ping on the surface of the 
water. . 

The wire B, by striking 
it at a point with the finger 
may be brought into vibration like a string of a violin. Then 
the floater C % will swing along the direction of waves set 
up in the wire. Such vibration, which causes particles to 
swing along the line of the direction of waves, is called longi- 
tudinal vibration. 




Fig. 125. 



ELECTRICAL ENGINEERING 277 

Ether waves 

227. Heat and light are supposed to extend from their 
respective sources, through the ether, toward other bodies 
which they heat or light by means of the transverse waves 
they produce in the ether. Heat sets up waves in the 
ether, and their presence may be demonstrated by holding 
the hand toward a heated object ; yet no heat will be felt 
when an iron or wooden plate is interposed between the 
hand and the heated object, a proof that the waves are 
deflected. Heat waves are longer than light waves, hence 
it is believed that the latter are merely heat waves of 
shorter length, as may be demonstrated by the friction of 
two substances which first give off heat and then light. 

Like the surface of the water disturbed by the dropping 
of a stone, according to their length and amplitude, the ether 
transmits either heat or light waves, in all directions. 

The frequency and length of ether waves varies. It is 
estimated, for instance, that light has a velocity of about 
185,000 miles per second. 

The immense velocity of the waves may be more 
clearly understood when it is considered that their velocity in 
one second equals a little more than seven times the circum- 
ference of the earth, or that these waves would travel a little 
more than seven times around the earth in one second. 

Ether waves due to electromagnetic disturbances 

228. The first experiments and researches regarding waves 
produced in the ether by electromagnetic disturbances, were 
made in 1865 by Clerk Maxwell, who constructed mechanical 
models to demonstrate electrical actions. Later, his models 
were improved by Professors Fitzgerald and Oliver Lodge, 



278 



MODERN ELECTRICITY 



who thoroughly studied the experiments of former scientists 
and prepared a series of important papers upon the results 
obtained. Prof. Lodge was the first who explained the 
actions of a Leyden jar by means of a hydraulic model. 
Even earlier, as far back as 1842, an American, Joseph 
Henry, suggested that the discharge of a Leyden jar might 
be of an oscillatory character. In 1847, Helmholtz stated 
the same supposition, which was proved to be true by the 
mathematical demonstration of Lord Kelvin in 1853 and by 
experiments of Feddersen in 1859. 

The syntonizing, or tuning together of the oscillator and 
resonator, may be compared to the adjusting of two tuning 
forks. The vibration of one fork produces sound waves, which 
in turn cause the other fork to vibrate. 

Professor Hertz, in 1888, actually produced electromagnetic 
waves in the ether by an apparatus, a diagram of which, is 

shown in fig. 126 
The apparatus 
consists of an in- 
duction coil A, 
to which a cur- 
rent is supplied 
by a powerful 
battery, B, in a 
manner similiar 
to that shown in dealing with Ruhmkorff's induction coils 
(see § 82). The secondary windings of this induction coil 
are connected with the so-called oscillator, by wires C and 
D, which consist of two brass rods E and F, terminating 
in small brass balls G and H. Large balls / and AT, are so 




ELECTRICAL ENGINEERING 279 

adjusted as to slide on rods E and F, respectively. The 
air space M, called the air gap, between the balls G and 
H, may be enlarged or diminished by moving the rods B 
and F. The resonator N, consists of either a wire rectangle or 
circle which terminates in two small brass balls, so that a 
small air gap O, is left between them. The oscillator may 
be brought in tune with the resonator by altering the posi- 
tions of balls / and AT. 

When a momentary current is sent through the primary 
windings of coil A, the current induced in the secondary 
windings produces a spark across the air gap M. This spark 
however, which has the appearance of a single flash, is in 
reality flying back and forth of the discharge between the 
small balls G and H, with intense rapidity. By this dis- 
charge a vibration is set up in the ether which by friction 
slowly dies away, similar to the waves on the water sur- 
face described in § 224. 

The electromagnetic waves set up in the ether by a 
spark passing over the gap M, extend in all directions ; but 
principally at right angles to a line that would connect the 
centers of the balls G and H. When the ether waves 
extending from gap M, pass through the resonator, elec- 
trical vibrations are also set up in the wire of the resonator 
which create a current in the wire and small sparks passing 
over the gap O, of the resonator are visible. No sparks, 
however, will be observed when the two apparatus, the oscil- 
lator and the resonator are not in perfect harmony; then 
the waves coming from gap M, interfere with the electrical 
vibrations set up in the resonator and disturb them. Com- 
pare the interference of waves described in § 225. 



280 



MODERN ELECTRICITY 





U 



j 



I 



j 



Bjerknes succeeded in obtaining curves showing the rapid 
subsidence of electromagnetic waves in the ether, by means of 
calculations based on the readings of an electrometer inserted 
between the balls of the resonator N. 

Fig. 127, shows the ex- 
tremely rapid subsidence of 
electromagnetic waves, when 
the oscillator and the resona- 
tor are not in tune. 

Perfect electromagnetic 
waves set up when the two 
instruments were tuned to 
syntonism, and when a ring shaped resonator was used are 
shown in fig. 128. ^r\r\r\(\r\(\(\ 

The coherer 

229. The resonator has 
proved to be of no use 
for detection of electro- 
magnetic waves sent over 
long distances. It was 
replaced by the so-called coherer, developed by Prof. 
Hughes,which after some improvements by Guglielmo Marconi 
is now used in wireless telegraphy. The Marconi coherer 
s x p cj /A fig- 129, consists of a 

-T - ■— Q ; V ; I1 "^> small glass tube A, about 

one-eight of an inch in 

FlG - 12a diameter and 1£ inches 

long, from which the air has been exhausted by means of a 

mercury pump described in § 185. Two silver poles B and C, 

are fitted into the tube so that a gap of about 1 ^ of an inch 



j 



Fig. 128. 



ELECTRICAL ENGINEERING 



281 



in length is formed between them. The gap D, is filled with 
granulated filings of an alloy of 96 parts of nickel and four 
parts of silver worked up with the merest trace of mercury. 
The electrical resistance between poles B and C, amounts to 
several thousand ohms, but when waves of a properly tuned 
oscillator pass through the tube, the filings are electro- 
magnetically attracted to each other, thus forming a con- 
ductor, of very few ohms resistance, between the silver poles. 
When the filings stick together by electromagnetic waves 
passing through the tube, they are said to cohere. Marconi's 
coherer is able to detect the merest trace of electromagnetic 
waves, is not liable to get out of order, and may be easily 
replaced when defective. 

Wireless telegraphy 

230. Fig. 130 shows 
the first receiving station 
for electromagnetic or 
Hertzian waves, which 
was constructed by Pro- 
fessor Popoff. When an 
electromagnetic wave 
strikes the vertical wire, 
it is conducted into the 
coherer, causing the 
filings to cohere, and thus 
between its silver poles. 




= EA8*TV 



reducing the enormous resistance 
A current from a battery is enabled 
to flow through the coherer, and then through the external 
circuit, where it energizes the magnets of a telegraph relay, 
thereby closing another circuit (not shown in illustration) con- 
taining a telegraphic recorder and battery. As soon as the 



282 MODERN ELECTRICITY 

relay is energized, the circuit of an electric bell is closed, 
its magnets also energized, and the bell-hammer striking 
against the coherer jars the filings apart, or decoheres them. 
If the waves are continuous they again cause cohesion and 
a working of the telegraphic recorder. 

This and the transmitting system was improved upon by 
Signor Guglielmo Marconi, who laid the first foundations for 
the practical use of wireless telegraphy. 

C 




Bi 

I'M'I 



D 

•= Fig. 131. 

Marconi's transmitting station in its earliest form, (see fig. 
131), consisted of an induction coil A, whose secondary 
coil terminals were connected with two small spheres B 1 and 
B 2 , which were separated from each other by a small air 
gap. Sphere B I was then connected with a long vertical 
wire, C, the sphere B 2t being connected with the earth 
by wire D ; When the Morse key E, was depressed, the 
current of battery F, flowed through the primary windings 
of induction coil A, inducing a secondary current which 
flowed to spheres B 1 and B2, maintaining a stream of sparks 
between them, as long as the key E, was pressed down. 
Thus produced, sparks set up electromagnetic waves, which 
extended in all directions in a form of wave shown in fig. 



ELECTRICAL ENGINEERING 



283 



128, which may be detected anywhere by means of a 
receiving station, the simplest form of which, was shown 
in fig. 130. These transmitting stations, however, do not 
answer the purpose very well, for which they were intended 
and the secrecy of messages transmitted through them, 
may not be guaranteed, as any receiving station placed any- 
where, will detect the electromagnetic waves sent by them. 

When it is desired to send waves in only one direction, an 
oscillator designed by Professor Righi, of Bologna, former 
teacher of Marconi, is 
used ( see fig. 132), in 
connection with a para- 
bolic reflector. (See fig, 
133.) This reflector con- 
centrates the waves in 
the required direction. 

When it is desired that the receiving station register only 
the waves coming from a certain direction, then the coherer 

is placed in the focus of 
a parabolic mirror which 
faces the direction. The 
arrangement is the same 
as in fig. 133, the oscil- 
lator being replaced by 
the coherer. Reflectors 
may not be used for trans- 
mitting messages over long distances. Experiments in which 
they were used were made over a distance not exceeding 
two miles. 

As shown in fig. 130 and fig. 131, a long vertical wire is 




OSGILCATOR 




„.- PARABOUC 
MIRROR 



Fig. 133. 



284 



MODERN ELECTRICITY 



used in connection with the transmitting and receiving stations. 
The effect of this Jong vertical wire is to increase the length 
of the electromagnetic waves set up in the ether, and thus 
enhance their power of penetrating obstacles, obstructing all 
waves of shorter length. It is supposed that the wave length 
equals about four times the length of the vertical wire employed. 
The vertical wires are generally suspended from high poles or 
wooden towers, the height varying according to the distance 
over which the signals are to be transmitted. Generally they 
are 150 feet high. Such a vertical wire is called "antenna." 

Marconi's Syntonic System of Wireless Telegraphy 
231. The fundamental systems of wireless telegraphy des- 
cribed in the foregoing § 230 may not be used for practical 
work because of the interference of simultaneous messages 
from different stations, every one of which sets the telegraphic 
recorders of all surrounding stations in motion # 
It also has been found that the receiving 
stations are affected by atmospheric disturb- 
ances and on such occasions, 
it was almost impossible to de- 
cipher the messages. To remedy 
this defect it was necessary to 
construct the two stations with 
a syntonized transmitter and 
receiver, so that the receiver 
would respond only to the im- 
pulses which are intended for it, 
and not be affected by the com- 
munications of other surrounding stations. Yet by syntonizing 
the two apparatus the strength of the electromagnetic waves 







n/WW- 

EARTH 



Fig. 134. 



ELECTRICAL ENGINEERING 285 

were weakened. Marconi constructed a transmitting station 
fig. 134, in the circuit of which there are two hollow cylinders 
A and B, one of which is inserted into the other and the inner 
cylinder B, being connected with earth, they act as a con- 
denser. The effect of this earthed inner cylinder is to increase 
the capacity of the oscillator. Later an induction coil was 
added into the circuit between the spark gap and the cylinders 
(so-called radiators). With, this arrangement the oscillation 
period of the receiving cylinder could be made so as to 
correspond with a single transmitter so that it would be 
affected by the waves coming from this transmitter only. 

This problem of perfect syntonizing two stations without 
affecting the strength and length of the waves has not yet 
been satisfactorily solved. 

Different systems of wireless telegraphy 

232. Many different arrangements of apparatus have been 
designed for successful transmission of messages through the 
atmosphere ; however, though the principle of wireless tel- 
egraphy specified in Marconi's patents — the production and 
detection of electromagnetic waves — is the foundation of all 
systems, it is quite important to know the characteristics of 
the most successful constructions. 

Fig. 135 shows the new arrangement of Marconi's stations. 
The transmitting station contains three separate circuits the 
first of which, consists of battery A, key B, and primary 
windings of induction coil C. 

The second circuit consists of secondary windings D, of 
the induction coil, gap E, condenser F, (to make the oscil- 
lations more powerful ) and the primary windings G, of a 
transformer which transmits the oscillation to the third circuit, 



286 



MODERN ELECTRICITY 



consisting of the secondary transformer coil H, one end of 
which, is connected to earth, the radiator I, with sliding con- 
tact K, (by means of which the inductance of the radiator 
may be varied) and the vertical wire L. 



a± 






Transmitting Station 



\d & m» 



£~ Fig. 135. 




-=£t 



[?)6 



r 



Receiving Station 




Transmitting Station 



T /2 

ReceivTna Stotiofl 

Fig. 136. 




The receiving station contains two separate circuits, 
one of which, consists of the vertical wire /, with the 
radiator /, sliding contact k y and primary coil h, of the trans- 
former ; the second, consisting of secondary coil g, of trans- 



ELECTRICAL ENGINEERING 



287 



former, the coherer e, parallel with condenser /, and battery 
a, in series with the telegraph recorder b. 

Fig. 136 shows a diagram of the arrangement of stations 
designed by Professors Lodge and Muirhead. 




Transmitting <§tatron 



Fig. 137. 



The apparatus of the different systems are named with 
same letters like those of fig. 135. The difference in the 
arrangement of the systems may be clearly seen from the 
diagrams. Fig. 137 shows diagram of stations designed by 
Professor Dr. Ferdinand Braun. 




Transmitting (Station 



WW 



Pecefv/ng St at ton 



■k — a a — Y 



3. 



+ 5 



Earth E«ot> 

Fig. 138. 



EflBTH 



These stations show instead of the usual connection 
^ith earth a well insulated capacity plate , M (m). Fig. 138 
shows the Slaby-Arco system. Fig 139, shows the Lee de 
Forest-Smythe system. 



288 



MODERN ELECTRICITY 



This arrangement differs considerably from all others. 
No condensers are used, and no induction coil. The cur- 
rent is supplied by alternator TV, the key B, being in the 
secondary circuit. 




Tra/rsm/twg § ran on 



C=10 

Receiv/no £ rat fan 



&m* EARTH 

Fig. 139. 



The receiving station shows instead of the telegraphic 
recorder, a telephone O, by which the operator hears ths 
signals telegraphed, whose waves affected the coherer. 



Questions and Answers. 

Q. Describe a portable apparatus for military services ? 

A. Both, receiving and transmitting stations are placed in a 
car, on the roof of which is a movable cylinder, instead of the 
vertical wire. A 25 centimeter spark coil is used, taking 
about 100 watts. The current is supplied by accumulators, 
which may be recharged by a dynamo placed in the car. The 
earth connection is established by a bare wire-net, which Is 
laid on the ground when signalling. This arrangement may bs 
successfully operated over distances of 30 miles. 



CHAPTER XV. 

Electroplating and Electro-Metallurgy 

Electrolysis 

233. As far back as 1801, Wollaston observed that a strip 
of silver when connected with another more positive metal 
and immersed in a solution of copper salts became covered 
with pure copper, and in 1840, Elkington successfully com- 
pleted his experiments of coating metals with a thin film 
of silver and gold, thus introducing electroplating, into com- 
mercial use. Yet, practically electroplating came into common 
use only a few years ago. 

Electroplating is the process of coating metal articles with 
thin films of other metals which are obtained by electrolysis 
from the solution of their salts. (Compare §45.) The articles 
which are to be plated are usually made of metals such 
as Britannia, brass and German silver, the coating being 
usually of gold, silver or nickel. 

Silver plating 

234. Silver plating is the most important branch of 
electroplating. The salts used in this process are chloride 
of silver, nitrate of silver and cyanide of silver. A standard 
solution for silver plating may be made in the following 
way : mix three ounces of silver chloride with water until 
a thin paste is made ; then dissolve nine to twelve ounces 
of 98 per cent potassium cyanide in a gallon of water; 
after doing this add the silver chloride paste to the solu- 
tion, meanwhile stirring constantly. The solution should be 

filtered before being used. In case a smaller quantity of 

289 



290 



MODERN ELECTRICITY 



the bath is required, the chemicals must be mixed so as 
to remain in the proportions, above specified. Great care 
must be taken to keep the proper ratio of current, silver 
and cyanide ; a weak current requiring more, a strong current 
less of cyanide. Free cyanide lessens the resistance of the 
solution ; too much of it causes a brownish color to appear 
on the plated articles, while an insufficient quantity of cyanide 
renders the plating irregular. 

Vats for silver plating 

2 35« For commercial silver plating, the vats are usually 
six feet long, three feet wide and two feet deep, generally 
made of wood, or if of iron, they are lined on the inside 
with wood. Fig. 140, shows such a vat, containing a 
solution in which a silver plate is immersed, and connected 

with the positive pole of 
the battery, thus serving 
as the anode, while the 
articles to be plated such 
as knives, forks, spoons, 
etc., serve as the cath- 
odes, and hang on looped 
pieces of insulated wire 
which are electrically con- 
nected to a copper tube, laid across the vat and connected 
with the negative pole of the battery. 

When a current is sent through this vat, pure silver is 
deposited on the cathodes, while an equal amount of silver 
is dissolved, and taken away from the silver anodes, thus 
rendering the solution always serviceable. In these vats, 
the silver anodes, only, must be changed when dissolved 




Fig. 140. 



ELECTRICAL ENGINEERING 291 

too much ; the solution does not require any change for a 
number of years. 

Nickel plating 

235. Articles, mostly machine parts, made of steel, iron, 
copper or brass, are usually nickel plated because of the hard- 
ness and durability of the nickel coating, which prevent the 
articles from oxidizing. 

The nickel plating bath is usually composed of the double 
sulphate of nickel and ammonia. The double salt is dissolved 
by boiling twelve to fourteen ounces of it in a gallon of water, 
and this solution is then diluted with water until a hydrometer 
placed in it stands at 6-5° to 7° Beaume. 

The nickel plating vats are usually made of wood and lined 
with lead. Carefully polished articles are dipped in a hot solu- 
tion of lye and water, and then in an acid solution as described 
in § 241 ; they are then hung in the bath, as are the articles 
to be silver plated, and thus act as the cathodes ; the anodes 
being plates of nickel. To improve the quality of the nickel 
deposit, an addition of 0-125 ounce of benzoic acid per 
gallon of solution is recommended. The current for nickel 
plating should be of moderate strength, from 0-5 to 8 ampere 
for every fifteen square inches of the article, the voltage vary- 
ing, from three to six volts being the most suitable. 

Copper plating 

237. Copper plating is mostly used for the purpose of giving 
iron articles a bronze finish, or to prepare articles for silver 
plating. The formula most commonly used at present is : To 
each gallon of water add five ounces of copper carbonate, 
two ounces of potassium carbonate, and ten ounces of potas- 
sium cyanide. The vats are of the same construction as those 
used in nickel plating, the anode being in this case a plate 



292 MODERN ELECTRICITY 

of copper. Before plating, the articles are cleaned with the 
solution described in §241. 

Gold plating 

238. The operation of gold plating does not differ much 
from that of silver plating. The bath is usually made of 
a solution of the double cyanide of gold and potassium in 
water, the solution being prepared in the same way as for 
silver plating. (See §234.) Baths for hot gilding should 
contain from ten to twenty grains of gold per quart of 
solution and a considerable excess of cyanide ; baths for 
cold gilding requiring from 60 to 250 grains of gold for each 
quart of solution. 

Current and pressure for plating 

239. The current for plating may be furnished by a bat- 
tery or by a dynamo generating a current at a low pres- 
sure. Resistances, in circuit with the coils of the dynamo-mag- 
nets, permit the adjustment of the pressure to suit the purpose. 
Too great a current renders the articles gray or brown and 
rough, while a small current plates well ; but if too bmall, 
it makes the operation of plating too slow. It was proved 
by experiment that the most serviceable current for silver 
plating is about one ampere for each sixty square inches of 
the surface of articles to be plated. The vats may be 
connected both in series or in parallel. 

Preparation of articles for plating 

240. Before submerging the articles to be plated in the 
depositing vat, they must be properly cleaned, and free from 
grease and oxides, which would cause the silver deposit to 
peel off. For this purpose, all articles must be polished 



ELECTRICAL ENGINEERING 293 

and thus all scratches removed. They are then dipped in 
a warm bath, consisting of a solution of caustic potash 
or soda in water. This cleansing solution may be prepared 
by dissolving commercial lye in water, and may be used 
for a great length of time. 

After the articles have been in this solution for awhile 
they are dipped in a bath of diluted acid, which renders 
their surface smooth, and then after having been carefully 
washed in running water, they are placed in the depositing 
vat. Great care must be taken not to touch any part of 
the articles to be plated with the fingers as they may 
thereby be made greasy, in which case they would not 
plate properly. 

Cleaning solutions 

241. The cleaning of articles before plating is done by 
means of solutions of acids , varying with the different 
materials of which the articles are composed. The solutions 
in general use are as follows : 

For copper and brass, 100 parts water, 50 parts nitric 
acid, 100 parts sulphuric acid, two parts hydrochloric acid ; 

For zinc, 100 parts water and 10 parts of sulphuric acid; 

For silver, 100 parts water and 10 parts nitric acid; 

For cast iron, 100 parts water, four parts nitric acid, 12 
parts sulphuric acid, and two parts hydrochloric acid; 

For wrought iron, 100 parts water, two parts nitric acid 
eight parts sulphuric acid, and two parts hydrochloric acid. 

Finishing of plated articles 

242. After having been plated the articles must go through 
a series of processes, namely, scratching, buffing and polishing, 



294 MODERN ELECTRICITY 

which are usually done by three different wheels, which 
rotate with great rapidity; one made of brass-wire, one of 
leather, and the other of canvas. Sometimes the articles 
are polished with the hand by means of steel or agate tools. 

Electrotyping 

243. Electrotyping which is now used in almost all large 
printing offices is the process of reproducing type and 
wood cuts by means of copper plating. First an impression 
of the type to be electrotyped is made on wax or soft 
paper pulp, which is done by pressing the wax upon the 
type. Then this impression is coated with fine plumbago 
so as to make it a conductor ; it is then hung in a copper 
plating vat, as described in § 237, where copper is deposited 
upon the mould. The thickness of this deposit varies 
according to the requirements of the type. The shell is 
then trimmed and backed up by a filling of melted type 
metal which is poured upon the back of the shell. Electro- 
typing has a great advantage in that it permits the set- 
ting up of large volumes with only a small font of type, 
which is always distributed after they have been electrotyped. 

Electrolytic refining of copper 

244. Refining copper is the most important application 
of electrometallurgy. Crude copper, the product of smelt- 
ing ores in ovens, usually contains many impurities, such 
as silver, gold, iron and lead, which greatly affect its con- 
ductivity ; There are about five per cent of such impurities 
in crude copper. By electrolysis these impurities may be 
easily separated from the copper, and thus electrolytic cop- 
per produced, which contains only such a small quantity 



ELECTRICAL ENGINEERING 295 

of other metals that it has a conductivity almost as high 
as (98 per cent) pure copper. Therefore almost all wires 
for electric work, as electric lighting, wires for winding 
armatures and magnets of dynamo-electric machines, and 
coils of measuring instruments are made of electrolytic 
copper. 

The copper to be refined is cast into large and thick 
plates, which are then hung in large electrolytic vats to 
serve as anodes, constructed as those described in § 237. 
Cathodes are thin sheets of pure electrolytic copper, which 
are arranged so as to be in alternate rows with the anodes. 
The electrolytic solution consists of copper sulphate (blue 
vitrol) with a trace of sulphuric acid, dilluted in water. 
The copper dissolving from the anodes replaces the copper 
from the solution which deposits on the cathodes to form 
thick plates of almost pure copper, which may be worked 
into bars or drawn into wires, so as to serve their purpose. 

The impurities contained in the copper of the anodes 
generally form salts with the electrolytic solution, and settle 
down on the bottom of the cells — this mud is called 
sludge. The silver and gold is then recovered from the 
sludge by smelting in ovens. Electrometallurgy is the cheapest 
method of separating gold and silver from copper. The 
largest electrolytic refineries are in this country, principally 
in the West, those in Montana being the most important. 

Current and pressure. 

245. The arrangement of the copper plates in electrolytic 
vats differs. In some cases they are connected in parallel ; 
in other instances in series ; the latter arrangement being 
more often met with, because it is more practical and does 



296 MODERN ELECTRICITY 

not require so many contacts as the former. Yet in 
the series connection, the leakage of current amounts to 
about 15 to 18 per cent. 

The pressure required, varies from 0*2 to 0*4 volt for 
each cell, the current from 10 to 16 amperes for each 
square foot of the plates. From 8 to 10 pounds of copper 
are usually deposited per kilowatt hour at a pressure of 
about 0-3 volt ; the cost of the process of manufacture 
amounting to about 07 cent for a pound of refined copper. 

In general, the pressure should be as low as possible, while 
a current of high intensity is needed. Too great pressure also 
causes the impurities to deposit on the cathodes, thus render- 
ing the deposit unsuitable for fine electrical work. 

Refining of silver 

246. When silver is to be recovered from copper, plates 
are cut of copper containing silver impurities, and used as 
anodes. Cathodes are thin silver plates slightly oiled. The 
electrolytic bath consists of a one per cent solution of nitric 
acid in water. The current causes formation of nitrates 
of copper and silver, by which action, copper and silver 
from the anodes are dissolved. From these formations silver 
is deposited on the cathodes, leaving the copper in the 
solution. Trays, placed under the cathodes serve to catch 
the silver deposit, which in the Moebius process is con- 
tinually removed from the cathodes by means of brushes 
which, mechanically driven, sweep over them. 

Reduction of aluminum 

247. The process of reduction of aluminum from its com- 
pounds was discovered by Hall (1886) in the United States 



ELECTRICAL ENGINEERING 297 

and almost at the same time by Heroult in France ; 
but aluminum cannot be gained from its salts by simple 
electrolysis of solutions of its salts in water, because 
the recovered metal immediately oxidizes after being deposited 
on the cathodes. In Hall's process which is used now 
in the Niagara Fall's refineries, the vats are made of iron 
and lined on the inside with carbon plates, which at the 
same time serve as cathodes, the anodes consisting of 
large carbon cylinders. The bath consists of molten cryolite 
brought to a temperature of about 1,600° to 1,800° Fahr. 
The aluminum oxide separates into aluminum and oxygen; 
the oxygen passes to the anode, combining with its carbon 
into carbonic acid; (carbon dioxide) The aluminum settling 
at the bottom of the vats is tapped off at regular inter- 
vals. The current used, generally has an intensity of 5000 
amperes, 7 to 8 volts pressure being sufficient. This current 
reduces one pound of aluminum for every 10 kilowatt- 
hours. 

Electric smelting 

248. That large electric arcs and their intense heat (see 
§ 172, 173, 174) may be used for chemical purposes was 
made known by the experiments of Depretz as long ago 
as 1848; yet their practical use for this purpose was no! 
made until 1880 when Sir William Siemens published a* 
interesting paper regarding his own experiments. 

In electric smelting the heat of the arc is utilized, by 
placing the ores to be melted between two great carbon 
electrodes in furnaces, built of fire-brick and lined with 
carbon. Electric smelting is used in the manufacture of 
calcium carbide, carborundum and for other purposes. 



298 MODERN ELECTRICITY 

Calcium carbide 

249. Calcium carbide, which is now widely used in gene- 
rating acetylene gas, was discovered by Moissan, a French- 
man, in 1892, and almost simultaneously by Thomas Wilson 
in the United States. 

In manufacturing calcium carbide, electric furnaces are 
filled with a mixture of burnt lime (calcium oxide) and 
pulverized coke or anthracite coal, this mass being heated 
to about 3000° by an electric arc. The calcium oxide com- 
bines at this temperature, with the carbon in the coke or 
coal ; the result of this combination being calcium carbide 
and carbonic oxide. The carbonic oxide passes away as gas 
and the calcium carbide after being allowed to cool off, is 
removed, ready for use. The calcium carbide is a gray hard 
crystallic mass, which when in contact with water gives off 
a gas of peculiar smell, — the now widely used acetylene. 
The largest calcium carbide works are those of the carbide 
company at Niagara Falls, where large furnaces are used, 
into which material is fed at one side, and the calcium car- 
bide taken out at the other. 

Carborundum 

250. Carborundum (silicon carbide) is also a product of 
the electric furnace, and is made by smelting a mixture of 
powdered carbon and sand. The result of this smelting is 
a mass of very hard black crystals, which are then worked 
up as grinding stones or other articles for similar use 

Electric welding 

251. The heat developed by large electric currents, over- 
coming resistances, is utilized for many purposes, the most 



ELECTRICAL ENGINEERING 299 

important being that of electric welding, an invention of 
Prof. Elihu Thomson. 

It was not before the year 1889 that electric welding 
was so improved as to be commercially valuable. 

The metals are carefully cleaned, and placed in espe- 
cially constructed welders with the surfaces which are to 
be welded together, touching each other. Then an alternate 
current of great intensity is passed through them, which 
brings the metals at the point of contact — the point of highest 
resistance — to the necessary heat; a mechanical pressure 
being applied at the same time, to press the metals together. 
By this process many metals can be welded ; even those 
metals which cannot be welded by any other method. 

Rail welding 

252. Electric welding is also used in electric railway work, 
to unite the joints of two rails, which, before this process 
of welding was developed, were bolted together. By welding 
the rails together expensive railway bonds may be dispensed 
with ; it also does away with the roughness in the track and 
the expense of repairing the rail-joints. 

Electric welders for rail welding are usually mounted on 
special cars, so as to move freely on the track. The current 
at 500 volt pressure is taken from the trolley and converted by 
means of a rotary converter, into an alternate current (of 

about 300 volts pressure) which is supplied to the welder. 

The rails are pressed against each other, while heating and 

cooling, with a force of about 35 tons. The current used 
is as high as 25,000 amperes. 



300 MODERN ELECTRICITY 

Electric heating apparatus 

253. It has been explained in paragraphs 61 and 62 that 
heat is generated by a current overcoming resistance. By 
passing through wires of high resistance, the current is made 
to generate heat, which is then used for different purposes, 
the more important uses being heating and cooking. 
Small heaters, usually installed in electric cars, consist of 
coils of insulated wire which offer a high resistance to 
the current. Electric kettles are now manufactured, having 
an electric heater of simple construction in their bases ; 
also electric flat-irons and curling-irons. They may be con- 
nected by a plug to the socket of an incandescent lamp. 
All electric heating apparatus are very desirable, because 
they do not vitiate the atmosphere. On account of their 
cleanliness, and the ease of handling and transporting them, 
they are especially convenient. They are not, however, liable 
to come into general use, on account of the expense of the 
electric current consumed by them. Assuming the cost of the 
electric current to be 10c for every kw. hour, and the effi- 
ciency of the heater 65 per cent, then the cost of heating 
a gallon of water from 10° to 100° C, would be about 5*72 
cents. The cost of heating rooms by electric heaters, 
in comparison with the use of coal, is enormous ; the 
cost of coal being less than 20 per cent of the cost of 
electricity. 

It is doubtful if electricity will even supersede coal for 
general purposes, unless it can be generated directly from 
fuel, without the intervention of steam engines. 



CHAPTER XVI.— X-Rays and Radium. 

Electric discharges in partial vacuum 

254. When an alternating current of high frequency is 
sent through a glass tube, from which the air has been 
partially exhausted, many beautiful luminous effects may be 
observed. For testing these effects vacuum tubes or Geissler 
tubes are usually employed. These tubes consist of thin 
glass blown into different shapes and are provided with 
two platinum electrodes, which are fused into the glass walls. 
Geissler tubes are only partially exhausted by a mercury pump, 
such as that described in § 185. These tubes may be worked 
with an induction coil, producing sparks about one half an 
inch long. 

The spark passes through entirely unexhausted tubes with- 
out producing any light effect. Yet a spark through partially 
exhausted tubes produces a peculiar, pale, tinted light which 
has a nebulous appearance. The cathode shows a bluish 
or violet light which as it extends toward the anode, 
loses its brightness. When Geissler tubes are filled with 
gases, as oxygen, hydrogen, carbonic acid, etc., the colors 
of the light differ from those obtained in a partial vacuum. 

Discharges in high vacuum 

2 55» When tubes are exhausted to a high vacuum, their 

glass walls become beautifully phosphorescent, but with this 

exception they remain almost dark. When articles, whether 

transparent or not, are interposed inside of the tube and in 

front of the cathode, then shadows are sharply projected on 

301 



302 



MODERN ELECTRICITY 



the opposite wall of the tube. Professor William Crookes 
made many important experiments (1874—1879) with partial 
and high vacuum tubes (Crookes tubes are shown in fig. 141.) 




Fig. 141. 

Roentgen's rays 

256. Professor William Conrad Roentgen of Wuertzburg, 
Bavaria, discovered in 1895 that a current passing through 
highly exhausted Crookes tubes, generated invisible rays 



ELECTRICAL ENGINEERING 303 

possessing peculiar qualities. Such rays pass freely through 
aluminum and zinc, through paper, wood and flesh, and 
excite a peculiar, brilliant fluorescence on plates covered 
with platinocyanide of barium. They also affect photographic 
plates in a manner similar to sun light. It was further 
observed, that rays possessing such qualities as described 
above, do not radiate from the cathode directly, but that 
they are given off from solid surfaces in the tube, against 
which the cathode rays (rays radiating from the negative 
electrode) are directed. Therefore small targets, usually 
made of platinum, uranium or osmium are placed in the 
tube so as to lie in the direction of cathode rays. These 
rays, as stated, pass through many substances, but lead 
platinum, glass, stone and bones are impervious to them. 
In honor of their discoverer they were called Roentgen-rays, 
and because of their mysterious qualities, X-rays which name 
in America has become more popular than the former. 

X=rays in medical use. 

257. When a specially constructed Crookes tube, (a few 
different varieties of which are shown in fig. 141), is brought 
to light in a dark room in front of a fluorescent screen, 
and the human body is interposed between the tube and 
the screen, the rays generated will penetrate the flesh, 
and show only misty outlines of it ; the rays, however, 
will be almcst completely obstructed by the bones, which 
will throw dark shadows on the screen. In this way the pres- 
ence of extraneous substances may be observed in living 
human bodies, without the necessity of using the surgeon's 
knife. X-rays are at present extensively used by physicians 
in locating foreign bodies and broken bones. 




Fig. 142. 
Shows abnormal growth of bone in the hand, as it appears on the screen. 



304 




Fig. 143. 
Shows a hand with shot located in the fingers. 



305 



306 



MODERN ELECTRICITY 



The fluorescent screen by means of which such effects are 
observed, is usually enclosed in a black box, and is called a 
fluoroscope. Two commercial forms of such a fluoroscope 
are shown in figs. 144 and 145. 




FlG ' 144 - Fio. 145. 

When, instead of the fluoroscope a photographic plate 
wrapped in black paper so as to protect it from sun-light is sub- 
stituted (see fig. 146) the 
X-rays penetrate the paper 
cover and produce on the 
plate a picture, called a 
radiograph, which may be 
developed and fixed in the 
usual manner of develop- 
ing and fixing photographs. 
The time of exposure 
varies greatly, depending 
upon the quality of the tube, the strength of the current and 
the transparency of the body to be radiographed. A brilliant 




Fig. 146. 



ELECTRICAL ENGINEERING 



307 



radiograph of a skull is shown opposite page 15. Time of 
exposure was only a minute. In this picture it may be seen 
(see dark spots) that some rays penetrated the bones of the 
skull and affected the plate, which in this case was an 
especially prepared radiographic film. Two nails which have 
been driven into the skull are shown by two white spots 
on the frontal bone. The long white line is an instru- 
ment which is inserted through the nose to operate in 




Fig. 147. 

the frontal cavity of the skull. A radiograph of a rat is 
shown in fig. 147. It clearly shows the bones of the rat 
darker than the flesh. Fig. 148 shows the radiograph of a 
human chest. X-rays though a recent invention, were adopted 
so rapidly in surgical practice that there is now hardly a 
hospital not possessing an X-ray outfit. 



308 



MODERN ELECTRICITY 



Radiographs 

258. The cathode rays project from the cathode, which 
usually consists of a small parabolic mirror on the anti- 
cathode, where they theoretically meet in a single point, 
and from this point, the effective X-rays are reflected. 
The sharpness of the radiograph depends upon the condi- 
tion that all rays are reflected from a single point of the 
anti-cathode. Rays reflected from any other point of the 




Fig. 148. 

anti-cathode cause the picture to become misty. Misty 
pictures are also the result when the cathode rays, meeting 
on a part of the glass tube, and not on the anti-cathode, 
emit X-rays. One may ascertain whether the radiograph 
will become sharp, by holding a lead pencil against the 



ELECTRICAL ENGINEERING 309 

tube and observing how distinctly the lead of the pencil is 
projected on the fluoroscope. 

The penetrating capacity of X=ray 

259. The X-rays have greater penetrating qualities, when 
the vacuum in the tube is almost perfect ; the more imperfect 
the vacuum, the less the efficiency of the X-rays, while 
the more perfect the vacuum, the greater the resistance 
of the tube, and therefore the greater the pressure of the 
current ( E=I R ), and the greater the penetrating power 
of the X-rays. 

Tubes producing rays of high penetration are usually said 
to be hard; those producing X-rays of low penetration are 
said to be soft 

The less its resistance, the softer the tube; and the lower 
the penetrating power of the X-rays, the greater becomes 
the current passing through and the greater the number of 
X-rays generated. Therefore they affect the photographic 
plate, which is placed behind the object to be radio- 
graphed, to a greater degree. 

Life of tubes 

260. The time during which tubes are able to produce 
effective X-rays is called the life of tubes. X-rays as sup- 
posed by modern scientists, are immeasurebly small gas-par- 
ticles which leave the tube, passing through its glass walls 
when a current is sent through it. Then the vacuum of the 
tube becomes more perfect. Therefore every tube is able 
to give only a certain amount of X-rays, because after a 
certain time, the vacuum of the tube becomes perfect, and 
the tube containing no more gases to emit, X-rays cease 



310 



MODERN ELECTRICITY 



to be generated. The life of the tube, therefore depends 
upon its size. In order to continue to use a tube the 
vacuum of which has become too perfect to generate X- 
rays, many different devices have been provided. These 
devices generally consist of small palladium tubes, or small 
mica plates, which are used inside of the tube 
(see fig. 149). When the vacuum becomes 
too great — the palladium being heated, usually 
by an alcohol flame from the outside of the 
tube, — draws the hydrogen from the flame, 
and transmitting a part of it to the tube, 
decreases its high vacuum, and thus renders 
the tube again serviceable. This process is 
known as Willard's method. 

The other method is founded on the prin- 
ciple that the mica plates become heated by 
the cathode rays and give off a small quantity of gases. 
Neither of these devices, however, work satisfactorily ; the 
amount of gases which they transmit to the tube being too 
small to replace the amount of gases consumed. The pro- 
cess of renewing the tubes, renders them softer. It is there- 
fore advisable to select tubes which possess renewing devices 
in preference to those without them. 




Fig. 149. 



Constancy of tubes 

261. The constancy of tubes is the quality they possess 
of maintaining their vacuum, and this depends greatly upon 
the manner in which the vacuum in the tubes has been 
produced. When selecting tubes, it is advisable to get 
those, which, when put into operation have a tendency to 



ELECTRICAL ENGINEERING 311 

become softer, in place of those which have a tendency to 
become harder. The softer the tube, the darker will be 
he shadows on the screen. 

The effect of X=rays on the human body 

262. The therapeutic effect of X-rays, need hardly be 
mentioned in a work of this character. This is a' distinct 
branch of medical science, of more interest to physicians 
then to electrical engineers, and the reader is advised to 
consult the numerous works upon the subject now on the 
market for a more exhaustive treatise upon the practical 
use of X-rays, for medical purposes. 

Radium 

263. Henry Becquerel in 1896 published the results of 
his experiments with invisible rays, which he had discov- 
ered in some preparations of the rare metal, uranium. 
Until 1898, nothing of importance was done in the way 
of adding to this discovery, when M. and Mme. Curie 
of Paris, published their very interesting papers on radium, 
a newly discovered metal, or chemical substance which, con- 
trary to all the rules of physics, emitted a peculiar light 
which made the surrounding atmosphere a good conductor 
of electricity. M. and Mme. Curie found that some minerals, 
containing uranium and thorium emitted such rays. Uranium 
is a metal of steel white color, which occurs but sparingly in 
nature, and is found combined in two comparatively rare min- 
erals, pitchblende and uranite, an emerald green ore. Thorium, 
which resembles nickel in its color, possesses about the 
same qualities as uranium. The energy of the rays given 
off by uranium is about three times the energy of the 



312 MODERN ELECTRICITY 

rays given off by thorium. The radio-activity of radium is a 
million times as great as that of uranium. At first, M. and 
Mme. Curie experimented with the pitchblende, chemically 
analyzed and separated it from the uranium and thorium, 
thus obtaining a substance, some of the rays of which were 
visible and about 400 times more active than those given off by 
uranium. This substance received the name of Polonium 
(from the birth-place of Mme. Curie). Later it was found 
that there was still another element in the pitchblende 
which emitted a vivid light, radioactive to a high degree, 
which received the name of radium. 

Qualities of radium rays 

264. The rays emitted by radium, usually called Becquerel 
rays, possess almost the same qualities as X-rays. They 
act on a plate of Calcium fluoride, rendering it. phosphores- 
cent, and radioactive, which means that the plate, after having 
been left under the influence of the radium rays for awhile, is 
itself enabled to give off radium rays. If a radium solu- 
tion is put into a small glass bulb, and then sealed, and 
immersed for a short time in distilled water, the water 
will become radioactive to as high a degree as radium 
itself. As far as has been observed, after such experiments, 
there would be no loss in the weight of the radium solution. 
Radium like electric sparks changes oxygen into ozone. 

When a diamond is left under the influence of radium 
rays for a certain length of time, it in itself, becomes 
radioactive, emitting light in the dark. Because glass and 
other crystals do not become radioactive, diamonds may 
be distinguished from imitations by testing them under the 
influence of radium rays. Recent experiments suggest the 



ELECTRICAL ENGINEERING 313 

possibility of changing the color of diamonds, by subjecting 
them to the influences of radium rays. 

The most important quality of radium rays is that which 
also gave to X-rays their importance : — that is, their action on 
photographic plates. The rays of radium appear to possess a 
greater intensity, demonstrated by the fact, that even when 
radium is enclosed in metal cases that X-rays could not 
penetrate, photographic plates become sensitive to their action. 
Radium rays produce peculiar burns on the skin, which in 
appearance are similar to those produced by X-rays. 

Nature of radium rays 

265. The nature of radium rays, like those of X-rays, 
electricity and ether, has not yet been discovered. Various 
hypotheses have been given which being in themselves 
based upon other hypotheses, are quite uncertain. The most 
credible explanation concerning the nature of radium rays 
is the following : — 

Radium, and other similar substances in lesser degree, 
act in a somewhat similar manner to transformers. In 
other words they are able to transform one kind of energy 
into another; i. e. for instance, drawing electricity from the 
air and transforming it into light. Another hypothesis is 
that the ether particles become subjected to rapid vibra- 
tion, thus generating light and heat. 

The almost total lack of loss in weight, compared with the 
enormous energy manifested, introduced with the discovery of 
radium, a problem that puzzled the world's scientists. 

It is very doubtful whether radium will ever become a 
commercial factor, but it has presented problems, the solving of 
which may revolutionize the accepted theories of physics. 



CHAPTER XVII. — Electrical Engineering. 

The most important work required of an electrical engines 
may be classified under the following three divisions : 

1. Selection of system, calculation and design of plant; 

2. Estimating the cost of erection of plant. 

a. Cost of horse power, produced at the station, 

b. Cost of transmission to place of consumption. 

c. Cost of distribution. 

3. Erection of plant. 

Under the first division, the design of power machines, 
apparatus, etc., should also be mentioned, yet this would 
include too much detail ; moreover, being a special phase 
of electrical engineering, upon which many books have 
been written, it has been omitted from this work. The 
first division, being first in importance will be treated 
at as great a length as necessary to give correct and 
reliable information covering cases that come up in ordinary 
practice. The second will be considered in its more impor- 
tant points. The third has been mentioned throughout the 
book ; a few important details however will be given in this 
chapter. 

Considering the branch of electrical engineering to which 
the above operations belong, we may classify them as follows : 

1. Electric railway engineering. 

2. Electric light engineering 

3. Power transmission engineering. 

314 



ELECTRICAL ENGINEERING 



315 



Electric railway engineering 

266. Suppose an electric railway is to be erected in a 
small town. The simple chart of this track is shown in 
fig. 150. The main line A-B-C, is to be double track ; all 
other branches single track. A-B. =25,000 ft. B-C. = 
4,000 ft., B-D =3,000, D-E. =3,000, D-F. = 10,000 ft. 
and F-G. = 12,000 ft., with a grade of four per cent.; the 
length of this grade being 5,000 ft. 



25000 



B 4000 C 
->< > 




DRAWN 



Fig. 150. 



52-8 


CI 


10 


79-2 


it 


15 


528 


it 


100 



Rise in feet with each per cent of grade : 

GRADE FOR ONE MILE FOR 1,000 FEET. 

£ per cent. 26*4 feet. 5 feet. 

1 •■ " 

10 «• •- 

Rise for other grades may be easily found by multiplication 
or division ; thus for 15£ per cent per mile, the rise equals 
52-8X1 5-5=8 18*40 feet. 

When calculating the conducting system for a line, as in the 
example, it is best to follow the steps mentioned on the next 
page. (Bell's method.) 



316 MODERN ELECTRICITY 

The extent of railway lines must be calculated. The track is 
to be mapped to scale, and all distances carefully noted. The 
railway lines which are to be built immediately may be drawn 
in heavy lines and the dotted lines may be used to indicate the 
proposed extension which may be built in the near future. 
Grades, their length and direction, and the proportion of 
length to elevation in per cent, is to be noted, (see fig. 150). 
Divide the road into sections, in such a way that all of 
them, under ordinary circumstances will have fairly constant 
service; in this case, double track, A-B-C one section, 
the other separate sections being B-E D-F and F-G. 

Calculate the average load on each section. Suppose that 
the town having a large population, will require 35, eighteen 
foot , single truck cars , each having a pair of 25 H. P. 
motors; line A-C, requires 20 cars, B-E, 6 cars, D-F, 4 
and F-G 5. In this case the electric center of gravity of 
the system, will be independent of the absolute amount of 
horse power which is required for each of 
the cars. 

The center of gravity is a point which 
must be found in a geometrical way, and 
represents the point in which the electrical 
loads have the same effect on the whole 
system, as if they were uniformly distri- 
buted, for example : There are three points 
a, b, c, (see fig. 151) with loads, 4, 2, 6, 
respectively ; connect two points, say a and 
b, by a line and divide thedistance between them, in (4 + 2 =) 
6 equal parts. The center of gravity of the points, a and b, 
will be in A % which is two parts distant from a and four parts 




B«> 



ELECTRICAL ENGINEERING 



317 



from b. (Which means that if a-b were considered the beam 
of a balance, supported at A, a weight of two pounds at b, 
would balance a weight of four pounds at a.) Then in the 
same way find the center of gravity of A (6) and c (6) by 
connecting them, and dividing Ac into (6+6=) 12 equal 
parts. Point B, which is the center of gravity of A and c, 
and at the same time the center of gravity of the whole 
system, lies 6 parts from A and 6 parts from C. 




Fig. 152. 



Find the center of gravity of this system (see fig. 152). 
Center of gravity of AC is in a. The center of BE. is 
in b, of DF, in c, of FG, in d. Because the load of every 
section is supposed to be uniform, the load of any section 
may be considered concentrated at its middle point. The 
center of gravity of points a, b, c, d, which in this case will 
be at the same time, the thereotical center of distribution of 
the whole system, is found to be O, as follows: — 

The center of gravity of c and d, is found in e; the center 
of gravity of e and b, in /, and the center of gravity of / 
and a in O. (If the start were made, not from c and d, 
but from any other two points, for instance from b and a, 



318 



MODERN ELECTRICITY 



the center of gravity of the whole system would also be 
found to fall in O.) 

Mark the distance of points a, b, c, d, from the center of 
distribution O. (see fig. 153). After the theoretical center of 
distribution O, is found, the distances Oa, Ob, Oc, and Od, are 
measured according to scale. 




Fig. 153. 

Distance Oa is 3500 feet, Ob, 9000, Oc, 6000 ft. Od, 
6750 ft. approximately. The weight of copper in the feed- 
ing lines for the different points on the main line is figured 
as follows: — 

For a. — Number of carsX amps, consumed by a single car 

, f distance of a from the center of distribution O. ) 2 oq 

X ! ■ — T7^ X 



L 1,000 J ' Drop in voltage 

The weight of copper in feeding lines for the whole sys- 
tem, equals the sum of the weights of feeding lines to 
all the points considered. If the center of distribution 
were shifted from the point (9, found in this example, the 
cost of copper in feeding lines would increase. The total 
weight of copper required for the feeding lines of this 
system is, when figuring with an allowable drop in line 
of 30 volts and when 25 amperes are needed by every car. 



ELECTRICAL ENGINEERING 



319 



for a 



for b 



for c 



ford 



20X25X 



6X25X 



4X25X 



5X25X 



[ 3500 
[1000 

[ 9000 

[Tooo 

[6000 



[1000 
T6750 



[1000 
33 



2 33 33 

X 30 = 25X 30 X245 

2 X^ = 25X^ X 486 



30 



30' 



33 33 

X 30 = 25X 30 X144 

33 33 

X — =25X — X229 
30 30 



C^-IX (245+486+144 + 229) 



For the whole system 

= 30,360 pounds of copper 

At 16c per pound for copper, the whole cost of copper 
in feeders for this system would be $4,857.60. 

The above figures are approximate ; because in practice, 
it is in many cases impossible to secure a suitable lot 
situated in the theoretical point of distribution, at a reason- 
able price and because the wires may not be spanned in 
straight lines. Sometimes it is more convenient to disre- 
gard the theoretical center of distribution, especially when 
material and power may be had cheaper at some other 
point, or when using the power of a distant water-fall. 

Now find the maximum load of each line. The power 
required at car wheels for a speed of about 8 miles per 
hour, (the most suitable speed for city railways) amounts 
approximately to 0-4 H. P. with additional 0*4 H. P. per ton 
for each per cent of grade, or to state a formula for estimat- 
ing : the total power required at car wheels of every maximum 
loaded car, equals the sum of the weight of the car body 
and the maximum weight of passengers multiplied by the 



320 MODERN ELECTRICITY 

sum [0-4 + 0-4 X per cent, grade.) In case there are no 
grades, the per cent is taken as naught. 

Assuming the car has a pressure of 500 volts, its efficiency 
from trolley to wheels about two thirds, it will be found correct 
to figure with \\ amperes per ton of the car loaded to its 
maximum capacity, and to allow 1^ amperes per ton for each 
per cent of grade. The maximum current may be considered 
as three times the average current, or in our example : — 







AVERAGE 


LOAD. 


MAXIMUM LOAD. 


[n section AC 


300 


amperes 


900 amperes 


«< >< 


BE 


90 


I ( 


270 


i< ii 


DF 


60 


li 


180 " 


II II 


FG 


65 


ii 


195 




Total 


515 


ii 


1545 



Then the maximum load of the whole track would probably 
never reach 1545 amperes, as the factors producing maxi- 
mum loads very seldom act on all sections at once. 

The trolley wire and the track return must now be con- 
sidered. A drop of 6 per cent may be allowed in the 
trolley wire (30 volts) and therefore No. 00 B & S being 
heavy enough will answer all requirements. The track 
return is quite an important factor for a good line, but 
supposing the rails are bonded well, it does not need to 
be considered. The sections of rail bonds in circular mils 
will equal (when dealing with 60 pound rails) thirteen times 
load times length of line divided by voltage. 

Now consider the feeding system ; for the central station at 
O (see fig. 154) and from A to C, there are two No. 00 trolley 
wires, from B to E, and D over F to G only one trolley 
wire. The length of the trolley wires fed by one feeder 



ELECTRICAL ENGINEERING 321 

will equal circular mils of the trolley times the allowed 
drop in volts, divided by thirteen times the load (33 being 
the constant for track return). In this example the length 
named above, for one car will equal 

133.000X 30 3,990,000 ^ A ^ t 

13X15 = -195- = 2 °' 462 f6et aPPr0X ' 
For two cars 10,231 ft., for four cars, 5,115 ft. etc. 

A B C 



Hence the feeder system may be arranged as shown in 
fig. 154. Here special care must be taken in regard to the 
grade on the end of the line F-G and B-E at E. More 
feeders must be provided there. The feeders measured 
from sketch amount to about 65,000 ft. of No. 000 weather 
proof feeder wire, weighing about 39,000 pounds and costing 
about $6,240.00. 

The trolley wire proper is about 

AB . . 2X25,000 = 50,000 

BC . . 2X 4,000 X 8,000 

BE 6,000 

DF 10,000 

FG 12,000 

86,000 feet long, contain 
ing about 34,400 pounds of copper and costing about $5,504. 0C 
The total cost of copper would be approximately, $1 1,744. 0( 



322 



MODERN ELECTRICITY 



including the feeders. The amount of power needed is 500 
(volts) X 515 (amperes average load) X 18 (hours per day) — 
4,635 kw. hours per day of 18 hours. At 2c per kw. hour, 
the daily cost of this would be $92.70 or approximately 
about $33,835.50 for the year. 

MATERIAL REQUIRED PER MILE OF TRACK 



NAMES OF ARTICLES. 



No. oo. B. & S. trolley 

No. ooo. B. & S. feeders 

7 strand No. 12 galv. iron span wire . 
7 strand No. 15 galv. iron guy. wire . 

60 pounds rails 

Joints 

Angle bars 

Bolts 

Spikes 5 X Y* i nc h 

Ties 

Bonds . 

Channel pins 

Poles, 125 feet apart 

Cross arms % X l % inches .... 

Cross arm braces, ^ X 8 inches . 

Lag screws for cross arms ^X 3 inches 

Lag screws for braces 

Eye bolts 

Hardwood pins 

Section insulators 

Turn buckles 

Chain insulators 

Plain ears 

Splicing ears „ 

Feeder ears 

Insulating caps 

Insulating cones 

Insulator holders 

Lightning arresters 

Section switch boxes ...... 



F 


or 




For 


Single 


Track. 


Double Track 


B-D-E, 


D-F-G. 


A-B 


-c. 


21 17 pounds 


4234 pounds 


466 


(< 


732 


(< 


760 


a 


760 


a 


300 


a 


450 


a 


94-3 


tons 


188.6 


tons 


360 


Dieces 


720 


pieces 


720 






1440 


a 


2160 






4620 


a 


7800 






15,600 


a 


2150 






4300 


a 


400 






800 


tf 


800 






1600 


a 


90 






90 


<< 


45 






45 


tC 


90 






90 


tt 


45 






45 


a 


144 






144 


a 


90 






90 


a 


45 






45 


« c 


2 






4 


C( 


90 






90 


(C 


90 




, 


90 


a 


45 






90 


(< 


1 






2 


cc 


10 






20 


a 


45 






90 


it 


45 






90 


ct 


45 






90 


a 


3 






3 


CC 


2 






2 


tt 



ELECTRICAL ENGINEERING 323 

The force required to lay this track consists of one en- 
gineer, one roadman, two gangs of men, each numbering 25 
laborers, with one foreman for the diggers, and one foreman 
for the track layers; also four spikers and three general helpers. 
This force would finish the road considered in the example, in 
about three months, each gang laying about 500 feet of single 
track per day. 

The tools for each of these gangs should consist of one 
small flat car, one portable forge, four cold chisels, one cross 
cut saw, one double handed saw, two monkey wrenches, two 
track wrenches, one complete set of track drills, one rail bend- 
ing machine, thirty picks with ten extra pick handles, thirty 
shovels (six short handled and twenty-four long handled), ten 
tampers, five wheel barrows, two track gauges, one level, one 
straight edge, five spiking hammers, four pair rail tongs, three 
crow bars, two spike claw bars, one reel line cord, braided, two 
six-pound hammers, one twelve-pound sledge, two axes, two 
adzes, 15 red lanterns (when working out of town, only six 
lanterns), one broad blade hatchet, six gallons of kerosene, one 
quart black oil, one squirt oil can, one box of lump chalk, and 
for the engineer and roadman, one engineer's transit, one 
leveling rod, ten surveyor's marking pins, and one steel tape. 

The cost of the material named above may be found 
easily, by consulting a catalogue and marking the prices 
there specified. The sum will give the cost of material per 
mile of single track and double track, and must be multi- 
plied by the number of miles of the system which is to be 
constructed to give the total cost of material for the whole 
system. Then the cost of tools, labor, surveying, drawings and 
estimates, traveling expenses of engineers and laborers, cost 



324 MODERN ELECTRICITY 

of property and franchise, etc., must be added. The cost of 
labor and material being subject to constant change is not 
figured in the above estimate. 

Cost of single railway tracks 

267. With 55 pound rails, the cost approximates $23,000 
per mile; with 75 pound rails, the cost approximates $33,000 
per mile. It is evident that these figures can not be exact for 
every system, as they depend upon several different factors; 
but they may be used safely in a preliminary calculation of 
cost. 

Notes for estimating on electric railways 

268. Approximate weight of trolley wires may be deter- 
mined as follows : 

Weight per mile of copper wire in pounds = (diameter in 
mils) 2 -*- 62-5. 

Resistance per mile in ohms is 54,892 -h (diameter in 
mils) 2 . 

Normal load is that at which the car motor will develop 
its rated H. P. when running at its normal speed on level 
ground. 

H. P. of motor = pounds of pull X miles per hour X 0-0027. 
Pounds of pull is the pull at the periphery of driving wheel. 

To start a standard car on a straight, level track requires a 
tractive force of about 1 18 pounds, and on curves about 225 
pounds, for every ton of total weight of car and load. 

To keep the car running at an average speed of six miles 
per hour requires a tractive force of about 16*2 pounds per 
ton of total weight. 



STANDARD TRACK SECTION 
CONCRETE / y C 

gauge: _ 

'l" 2 "SAND 




POLES AND BRACKETS WITH SINGLE 
ARM FOR SINGLE OR DOUBLE TRACK 

INSULATORS FEEDERS 



FOR USE IN CITIES WITH DOUBLE 
ARM FOR DOUBLE TRACK 




ARM OF POLE ADJUSTED FOR DOUBLE TRACK 



^TROLLEYS 



TROLLEY WIRE SUSPENSION CURVES 
SINGLE TRACK DOUBLE TRACK 

-TROLLEYI) 11^ POLE 





Fig. 155, 



326 MODERN ci.ECTRICITY 

WEIGHT AND CAPACITY OF CARS. 



DESCRIPTION 


Weight of 
car 


Length over 
platforms 


Maximum load 
and 




in pounds. 


in feet. 


seating capacity. 


4-wheel baggage car 


5,000 


12 


16,000 pounds. 


3-wheel " " 


5,500 


14 


20,000 " 


Regular passenger " 


3 5 50 


24 


50-60 passengers 


Passenger car for suburban 








service 


10,000 


25 
31 


40-50 " 
70-90 ■ * 


Open car 


9,600 





These cars require from 5,000 to 12,000 watts for a speed 
of eight miles per hour. 

All the cars specified are for United States standard gauge 
tracks, which are 4 feet 8^- inches wide (measured inside the 
rails, as shown in the standard track section in fig. 155). 

Railway curves 

269. The curves of railways are usually stated in the degrees 
of their angle of declination from a straight line. 

A curve of 1° (degree) has a radius* of 5730 feet. 



A curve of 2° has a radius of 



A curve of 10° has a radius of 



A curve of 50° has a radius of 



5730 I „ ft ' 
-V- = | 2,865 feet, 



I 2 
[5730 



I 10 

f 5730 
50 



573 feet. 



114 feet. 
J 



Curves should be made with the greatest possible radius, as 
they add greatly to the resistance of a car, due to friction of 
the wheels on the rails. A 200° curve adds about as much 
resistance as a five per cent, grade. 



*Radius equals one-half of diameter. 






ELECTRICAL ENGINEERING 327 

Elevation of outside rails on curves 

270. For a United States standard gauge track (4 feet 
8^- inches), the elevation of the outside rail in inches above 
the horizontal plane = 178X (the square of velocity of car in 
feet, per second) -*- (the radius of curve in feet). 

Power station 

271. The proper location of a power station is affected by 
various factors, the most important of which are: — the cost of 
copper for feeders, the cost of coal, and the cost of water. 
Taking these factors into consideration, the value of the pro- 
perty may be determined. If it chances that a suitable piece 
of property lying in the center of distribution of a system can 
be bought, it is wise to pay even a high price for it, if 
necessary, as it makes possible the cheapest kind of distribu- 
tion, and saves not only in the cost of copper but in the cost 
of power. Every mile separating the central station from the 
center of distribution, increases the cost of copper and power. 

Special attention must be paid to the cost of handling coal. 
A piece of property lying near railway tracks, from which it is 
allowable to run a side track into the station, so that the coal 
may be delivered directly from the cars into the bins,would offer 
a great advantage. It is very unsatisfactory to pay extra for the 
work of re-handling the fuel, and often very detrimental to the 
interests of a company, as the loading and forwarding a ton of 
coal over a distance of one mile or less, costs from 18 to 30 
cents. The station of a system similar to that considered in 
the foregoing example, would need at least nine tons of coal 
per day, and the cost of re-handling the coal, not figuring 
the shrinkage in weight, would add more than $720.00 to the 
yearly expenses. 



328 MODERN ELECTRICITY 

Another important requirement, is the nearness of the 
source of cheap water supply. The station mentioned in the 
foregoing example, would annually consume in its boilers, 
approximately, 535,000 cubic feet of water. In cities where 
water must be bought at $1.00 per 1,000 cu. feet per annum, 
this extra expense of the central station would amount to 
about $535.00. When possible, the central station should be 
near the car-barn, but at such a distance, that a fire in the 
central station could not ignite the barn or cars within it. If 
the car-barn is situated too near the central station, the cost 
of insurance is increased. 

Before figuring on the foundation for the station house and 
the cost for machinery, careful tests must be made to deter- 
mine the quality of the ground upon which they are to rest. 
It is advisable to make borings at a few different points. 

These borings are made with piles which are driven into 

the soil by a ram of known weight. The extreme load 

per sq. foot (the load per sq. foot which would cause sinking 

of the ground ) may be determined by using Trautwine's 

formula : 

Extreme load (in tons) = 

Cube root of fall ^ wt. of ram v n m „ 
in ft. (of hammer) in pounds 



last sinking of pile in inches + 1 
This would show for a fall of 8 feet, weight of ram 1,000 
pounds and sinking 0-25 inches an 

'"8~X 1000 X 0-023 2 X 1000 X 0.023 



extreme load = 



025 + 1 0-25 + 1 

46 

— - = 36*8 tons. 

IAD 



TERMINAL ANCHOPAGE OF SINGLE TRACK TROLLEY 




SINGLE SUSPENSION FOR WOOD .POLES 




TURNOUT FOR SINGLE TRACK RAILWAYS 





METHODS OF CONNECTING FEEDER TO TROLLEY 
FEEDERS 




w y-jumper 



TROLLEY 



13 



insulator/spanwire 



FEEDERS 



feeder tap 




-e*®- 



SPANWIRE 



Fig. 156. 



330 MODERN ELECTRICITY 

Allowing a safety of 2, 18*4 tons would be the safe load 
per square feet. 

The bearing power of different soils, ranges from 30 tons, 
(for hard rock,) to one ton, (for quick sand,) per square foot. 
The foundations for machinery should be built of good con- 
crete ; the foundations and walls of the station of good brick, 
stone or concrete ; the roof trusses of steel and the covering 
of corrugated iron. Of course the cost of the central station 
depends upon the material used, depth of foundations, etc. 

Electric light and power transmission 

272. It is almost impossible to give examples under this 
heading which will enable the reader to use the figures given 
below in practical estimating. The wires may never be drawn 
in straight lines ; the number of poles, insulators, switches, 
etc., vary considerably with the locality or the shape of the 
rooms in which electric light is to be installed. The amount 
and cost of labor also varies to such a degree that it is 
impossible to state a definite amount of work which may be 
performed by a "wire-man" in a day, or the cost of labor 
for installation. 

It is wise to thoroughly examine the locality where the 
ielectric light is to be installed, and to consider all circum- 
stances carefully. The examples given below, will give the 
reader an idea of how to calculate the details for electric wir- 
ing for light and transmission purposes, and the authors hope 
this will prove of considerable value to all those who are 
engaged 'in electrical engineering. 

When considering incandescent lamps, it must be remem- 
bered that all the requirements of lamps must be fulfilled to 



ELECTRICAL ENGINEERING 331 

assure proper working of the plant, with a maximum light, at 
a minimum expense. 

Proper use of an incandescent lamp requires : That the 
lamp be supplied with not more than its rated voltage ; that 
the voltage be kept constant ; that dimly burning lamps 
be immediately replaced, because lamps burning after they 
cease to give good light, waste considerable power. 

If a 16-candle power lamp burned properly for 1200 hours, 
and then was used for an additional 600 hours, it would con- 
sume the same amount of current, yet the light it would give 
would equal only about 8-candle power. If the current be sup- 
plied at a cost of 0.55c per lamp hour, the total cost of cur- 
rent for the entire 1800 hours during which the lamp burned, 
would equal 1 800 X 0.55c or $9.90. If instead of this lamp, 
three other 800 hour rated lamps were used, each of them 
costing about 20 cents, the average light would have been 
doubled at an increased expense of not more than 40 cents 
or about 4 per cent, of cost of current, and the customer 
would receive a light 100 per cent, better, as one new lamp 
gives twice the light of an old one, at one half the cost of 
current. 

In figuring on the life of lamps, 600 hours should be taken 
as the maximum. A station supplying 100,000 lamps of aver- 
age life, not exceeding 600 hours, would have to exchange 

100,000 ; - , 

■ — — — — or 166 lamps in a month. 
600 y 

Energy required for an incandescent lamp equals the product 
of square of the current and hot resistance. 

Thus for a lamp of ^ ampere and 220 ohms hot resistance, 
the energy required equals 0*5 2 X220 = 0-25X 220= 55 watts. 



332 MODERN ELECTRICITY 

Heat units required for an incandescent lamp of 110 volts 
and 0*5 amperes in 10 minutes equals 

1 10 X 0-5 X *24 X 600 = 792 calories. 

Average cost of light for a 16 c. p. incandescent lamp per 
hour varies from $0,003 to $0.02. (When burning 10 hours or 
£ hour per day ) 

Average cost of 2000 C. P. arc lamps per hour varies from 
$0.02 to $0.18. (When burning 10 hours or only £ hour 
each day.) 

EXAMPLE 71. 

In a large building, 300 lamps are to be fed by a circuit 100 
feet long at a loss of 6 per cent. Each lamp requires 110 
volts and 5 amperes. The size of the main wire is to be 
calculated. 

Resistance of a wire equals the constant of the material 
of the wire used, times the quotient of its length and area of 
cross section. The constant of commercial copper is taken 
as 10*8. The circular mils of the wire equal the quotient 
of 10-8 times the length of the wire and resistance. The 
resistance of any number of lamps in parallel, equals the 
quotient of the hot resistance of one lamp, divided by the 
number of lamps. 

The section of the mains in circular mils equals the pro- 
duct of 10-8, twice the length of the mains, number of lamps 
and 100 minus per cent, drop in mains, divided by the pro- 
duct of the hot resistance of each lamp and the per cent, 
of drop in mains. 

The hot resistance for 110 volt lamps is 220 



ELECTRICAL ENGINEERING 333 

Substituting figures in the example, the section in circular 
mils of the main may be found 
„ , .. 108X2X 100 X 300 X( 100-6) 
Circular mils = 2 20 X 5 = 55 ' 374 

circular mils, which corresponds to No. 2 B. & S. gauge. 
The whole length being 2 X 100 = 200 ft., the weight of 
this wire in weatherproof insulation will be 50 pounds. (250 
per 1000 ft.) and the price about $20.00. The number and 
cost of other articles necessary for the construction of the 
circuit in this example, depends largely upon local circum- 
stances ; therefore no attention need be paid to them. 

EXAMPLE 72. 

50 electric arc lamps are supplied by direct current of 
9 8 amperes and E. M. F. of 42*5 volts at the terminals of 
each lamp. The resistance of leads is 3*2 ohms. The dynamo 
delivers 38*45 H. P, at the armature which has a resistance 
of 23*5 ohms. 

1. What is the amount of power consumed by each 
lamp? 

2. What is the amount of power lost in the circuit ? 

3. What is the total power expended ? 

4. What is the total E. M. F. ? 

5. What is the mechanical efficiency ? 
Answer. 

i. The power consumed by each lamp = volts X amperes 

42-5X9-8 = 416-5 watts; 416 ^ y atts = Q . 55 H> p< 

746 

2. The power lost in the circuit, equals square of cur- 
rent multiplied by the sum of resistances (here : the resis- 
tance of the armature and resistance of the leads) = 



334 MODERN ELECTRICITY 

98 2 X (23-5 + 3-2) = 96-04 X 267 = 2564-268 watts 

2564-268 n n T T n 
ar.--^_-3-43 H. P. 

3. The total power equals the power consumed by one 

lamp multiplied by the number of lamps, plus power lost in 

circuit = 

50 X 0-55 + 343 = 30-93 H. P. 

4. The total E. M. F. equals the product of current and the 
sum of resistance (here : resistance of the armature and resis- 
tance of the leads) plus product of terminal voltage of each 
lamp and number of lamps = 

9-8 X (23-5 + 3-2) + (50 X 42 5) = 2386*66 volts 

5. Mechanical efficiency equals the quotient of the energy 

consumed by one lamp times number of lamps, plus energy 

lost in the circuit, and the energy delivered at the armature of 

dynamo = 

50 X 0-55 + 3-43 __ 3093 _. nQn 80 Qn 

■ — — 080 = = 80 per cent. 

38-45 38 45 100 P 

EXAMPLE 73. 

A direct current of 50 amperes is to be transmitted. The 
cost of one H. P. is $0,005 ; the price of a cubic centimeter 
of copper is $0,006, and its specific resistance is 0.00000157. 
What section (in square centimeters) must the copper conduc- 
tor have in order to transmit the energy most economically? 

Answer. — The work done per second by the current in a 
conductor, one centimeter long, in 

. . 50 2 X 0-00000157 

joules = ; : — — , which corresponds to 

section of conductor 

50 2 X 00000157, 

Horse Power ■ A , , : ; , per second. 

746 X section of conductor 



ELECTRICAL ENGINEERING 335 

This work is lost because it is converted into heat, thus 
causing a loss, amounting to 

d ,50 2 X 00000157 X 0-005 

$- ; per second. 

746 X section of conductor 

And if the work lasts ten hours a day, or 36,000 seconds, tht 
daily loss will amount to 

50 2 X O'OOOOO 1 57 X 0-005 X 36,000 
746 X section of conductor 

or in a year of 365 days at 10 hours each. 

^50 2 X 0-00000157X0-005 X 13,140,000 

3 — — — - — ■ 

746 X section of conductor 

Price of one cubic centimeter of copper is $0,006 ; price o* 
one centimeter length of conductor will be $0,006 X section 
of conductor, and a loss must also be figured of at least 

0-006 X section of conductor 

$ 20 ' 

accounted for interest on capital. 

Therefore, the total loss per centimeter length of conductor 
per year will amount to 

.502X 0-00000157 X 0-005 X 13,140.000 , 
746 X section of conductor 

0-006 X section of conductor 
20 

The loss is at minimum when the sections of conductor 
equal (Thompson's formula) : 

J 20 X 000000157 X 0.005 X 13.140,000 = 
* " 746X0-006 



336 MODERN ELECTRICITY 



206298 X 0- 1 2-06298 0.4625 

. 50XV tt^ = 50XV ■ A An -50XV 

1 4-4/ 4-47 

= 50 X 0*68 = 34 sq. millimeters. 

When dividing by it = 3-1416, 

the square of radius of the section of wire is found to be 

34 

= 10.82, from which the radius equals V 10 82 = 

2*21 millimeters, or 87 mils (about No. 1 1 of B. & S. gauge). 

EXAMPLE 74. 

A system of lighting is to be installed in a theater, and 250 
lamps, each 110 volts and 5 amperes (hot resistance of 
each .220), are to be fed by a circuit 200 feet long; five per 
ceni. drop is allowed. Calculate the size and cost of wires 
when a three-wire system is used instead of a two-wire system. 

With two-wire system : 

specific twice the number 100 — - 

section of resistance X length of X °^ X P er cent, 

wire in = f CO pp e r circuit lamps drop 

circular mils — ; ; ; ; — ; : 

Hot resistance or a single lamp X P er cent, drop 

108X2 X 200 X 250 X (100-5) . - 

= = 93,272 cir. mils, which 

2z0 X o 

corresponds to No. 0, B. & S. gauge. 

When two dynamos are used, one terminal of. each being 
connected to one of the circuit wires, the common junction 
being connected to the third wire, three wires are required, 
(see § 156). In such a circuit, two lamps are in series between 
the positive and negative wires, and therefore require only one 
half of the current which an equal number of lamps would 
Y equire on the two-wire system. The voltage between the 



ELECTRICAL ENGINEERING 337 

outside wires is twice that of the two-wire system, the current 
being only one half of the current of the two wire system. 
Therefore for a given drop, the drop of voltage in this system 
will be twice that of the two-wire system ; the resistance is 
four times that of the two-wire system, and therefore the cross 
section of any of the three wires equals only one fourth of the 
cross section, determined for the two-wire system. 

The middle, neutral wire might, if necessary, be made of a 
smaller cross section, yet it must be remembered that it has 
to carry the excess back to the machine if the numbers of 
lamps on both sides of it are unequal. 

Considering all three wires of equal cross section 

93 272 

• — : = 23,318 circular mils, or No. 7 B & S. gauge, 

the total amount of copper needed for the three-wire sys- 
tem is only three eighths of the amount of copper for the same 
number of lamps on a two-wire system. The circuit for the 
two-wire system is 

2 X 200 = 400 feet of No. B & S. and costs about 
$84.00, and for the three-wire system, 3 X 200 =» 600 ft. of 
No. 7 B & S. and costs about $42.60, when using rubber 
insulated wire. 

This shows a saving of $41.40 in the three-wire system. 
Yet this saving is considerably diminished by the extra cost of 
installing and the extra cost of using two machines instead 
of one.* 

EXAMPLE 75. 
800 lamps, rated 1 10 volts, 0*5 amperes, are suppl'ed with 
direct current through circuit 500 ft., long at a loss amount- 

* Se^e diagrams No. I and II, and explanation given in the appendix. 



338 MODERN ELECTRICITY 

ing to 6 per cent. Calculate the size, the weight and price of 
the wire. 

Answer, Section of wire in circular mils = 

Constant (2 1 60) X watts delivered to lamps X length of circuit 

square of E. M. F. lost in line X per ct. watts at the lamps 
For this example (the factor being 2 1 60) 

e 4 . r . . ^ AA 2160X800X0-5X110X500 

Section of wire in CM.= -— r — --— ; 

110 2 X 6 

_ 47,520,000,000 



= 65,454 CM, 



726,000 
corresponding to No. 2 B & S. 

Volts lost in circuit = 

E. M F. at lamp end X per cent watts lost in circuit 

' Too 

110X6 660 , _ . 

= 77^~ = tt^; = 6-6 volts. 

100 100 

Weight of copper = 

Constant v watts delivered ^ Constant ^ square of length 
6-04 X to lamps 2160 X of circuit 

sq. of E. M. F. at lamps X per cent, watts lost in line X 10 6 

_ 6-Q4X800X HOX 0-5X2160X500* 
110 2 X6X 10 6 

143,510,400,000,000 1,435,104 tM r 

*nr,, r.r,r, r,r,r. r,r,r, = ~, * , r. ~~ 197*6 pOUndS CODDer. 

726.000,000,000 7260 v ^ 

at $0.35 per lb., the cost of copper is 197-6 X 0-35 = $69.16. 

EXAMPLE 76. 
In a water power station, a four wire line is installed to 
transmit 2500 horse power over three miles to a sub-station, 



ELECTRICAL ENGINEERING 339 

containing step-down transformers The current is two phase 
alternate current with 40 periods frequency. 

The E, M. F. of the generators in the power station is such 
as to result in 5,000 volts at the primaries of the step-down 
transformers. Line loss is 8 per cent , of delivered power ; 
transformer efficiency 97 per cent., and load of such character 
as to make the power factor about 80 per cent ; calculate sire 
of the circuit, and cost of copper. 

Answer. Power at secondary coil of transformers = 

2500 H. P or 2500 X 746 = 1865 kw 

Power at primary coil of transformers 

1865 X 100 ,^« , , 

— = 1922-6 kw. = 1.922,600 watts. 

97 

Loss due to transmission 8 per cent., 
therefore the section of circuit in circular mils equals 
Constant 1690X watts delivered X length of line in feet _ 
sq, of E. M. F. X per cent., of power lost 

1690X 1,922,600 X 3X 5280 = _ 51,467,232,960,000 
5000 2 X 8 200,000,000 

514,672-3296 



= 257,336 circular mils. 



2 

Taking four No. 2 wires (66,370 cir. mils.) in parallel the 
area of section = 4 X 66,370 = 265,480 cir. mils. 

With this arrangement 4X4= 16 No 2 wires are used 
and the per cent loss is, 

Constant v watts length 
1 690 X delivered X of line _ 1690X 1,922,600X3X5280 
sq. of ^ area of section of ~ 5000 2 X 265,480" 

E. M. F conductor 



340 MODERN ELECTRICITY 

_ 5 1,467 ,232,960,000 5,146,723.296 



6,637,000,000,000 663,700,000 



= 7 76 per ci 



Therefore the power lost in transmission equals 
2 500X776 



00 



194 H. P. 



Constant*^ E. M F. at per cent, of 

, ,_ w ^ 110 transformers power lost 
Loss of E. M F = — —— 

1-10X5000X8 AA „ . 

— — = 440 volts. 

100 

E. M. F. of generator = 5000 + 440 = 5440 vults. 

Constant 0*625 X power in watts delivered 



Current in line = 



E. M. F 
0-625 X 1,922,600 



=240*325 amps. 



5.000 
Core loss in transformer, . . 1-5 per cent. 3-604 



Total current, 243.929 " 

Weight of copper in pounds = 

r- 10^0 x/ watts ^ ~ . -, nn w sauare of length 

Const. 2 C8 X j ,. ,X Const. 1690 X - ( . ,. & 
delivered of circuit 

sq. of E. M. F. X per cent of power loss in transmission X 10 6 

12-08 X 1 .922 600 X 1690 X (3 X 5280) 2 ^ 
5000 2 X7*76X 10 6 

11,421,477,751,799,808,000 M M „ , £ 

- — ,~ , ^^ ^^ ^^ ^^ = 58,870 pounds of copper. 

194,000,000,000,000 ' FK 

and taking $0.35 as price of one pound of copper, the cost of 
copper is 58,870 X $0 35 = $20 e 604 50. 

* Tins constant is suitable only for alternating current of 40 cycles ; power 
factor being 80, and wires No. 2-18 inches apart. 



ELECTRICAL ENGINEERING 



341 



EXAMPLE 77. 
A large factory has a single phase, alternate current, three- 
wire system installed, with a frequency of 60 cycles. The 
power station contains a generator A. (See fig. 157.) 




Fig. 157. 

The power is transmitted by three wires to secondary coils 
of transformers, B x> B 2i B 3> The distance from generator to 
transformers is 1 ,000 feet. The secondary current feeds two 
twenty H. P. induction motors ; the distance from these 
motors to transformers is 300 feet ; 1500 lamps, E, rated 
at 1 10 volts and 0.5 ampere ; the center of lights is 250 feet 
from transformers. Drop in primary mains, 3 per cent ; drop 
in secondary mains about 10 volts; drop in transformers 3*5 
per cent. ; the energy lost in transformers amounts to 3 per 
cent. ; the efficiency of the indnction motors amounts to 
85 per cent. Calculate the details of this system 

Answer. 

1. For light : 

The power needed for lamps = 1500 X 0.5 X 110 = 82,500 
watts. 



342 MODERN ELECTRICITY 

For 10 volts loss in secondary mains, loss of power = 

volts loss X 100 _ IPX 100 

constant 1-34X E. M. F. X 2 ~~ 1-34X 1 1 1 X 2 . ' P 
Section of conductor in circular mils = 

constant 2400 X power delivered in watts X length of circuit 
square of E. M. F. X per cent, loss of power. 
Section of conductor == 

nj#w , 82,500X250 49,500,000,002 „ rtni „ . 
2400X 220^X3-3 = 159,720 = 3 ° 9 ' 917 « ^ 

Take 3 No. wires, B. & S. gauge (area= 1 15,534 cir. mils). 

Total area of section = 3X 105,534 = 316,602 cir. mils, 

Loss of power in per cent. = 

constant 2400 X power delivered in watts X length of circuit _ 
section of conductor X square of E. M. F. 

2400 X 82,500 X 250 _ 49,500,000,000 

316.602X220 2 "~ 15,323,536,800 ~~ ' P er cen * 

E. M. F. X p. ct. loss of power 



Drop in voltage = const. 1 .34 X 



100 



220 X 3*2 
= 1-34X — r^r — = 9-43 volts or approximately, 9 volts. 

E. M. F. at the secondary coils of transformers = 220 + 9 = 
229 volts. Current in secondary lighting circuit = 

constant 1 -052 X watts delivered __ 82,500 __ 86,790 

E. M. F. == ' 220 = 220 

= 395 amperes. 

The two outside lines may each consist of three No. 
3. &S., and the neutral (center) line of (one-third of the 
outside lines) one No. (B. & S.) wire. 



ELECTRICAL ENGINEERING 343 

Length of wire in outside line = 3 X 250 = 750 ft. of No. 
B.&S. 

Length of wire in second outside line = 3 X 250 = 750 ft. 
of No. B. & S. 

Length of wire in neutral (center^ line = 1 X 250 = 250 ft. 
of No. B. & S. 

Total length of No. B. & S. wire equals 1,750 feet. 

Weight of copper in 1,750 feet of No. B.&S. wire 
(0-3195 lbs. per foot) = 0*3195 X 1750 = 559-125 lbs. 

2.) for motors. 

H. P. of motor X 746 X number of motors 



Power needed = 



efficiency 
20X746X2 



85 



35.106 watts, 



35,106 
or on each circuit = — — = 17,553 watts. 

Power factor 80 per cent. Drop on motor circuits 3-5 per ct. 

Area of section of conductor 

power in watts X length of circuit 



= const. 3380 ) 
= 3380 X 



sq. of E. M. F. Xper ct drop 
17,553X300 



220 2 X 3-5 

17,798,742,000 irNr ^ n . , 

= , ,rs A^r, =105,068 circular mils. 

169,400 

Take one No. wire (B. & S.) area= 105,534 cir. mils. 



344 MODERN ELECTRICITY 

Per cent, loss of power = 

power delivered in watts X length of circuit 



const. 3380X 



sq. of E. M. F. X area of sec. of conductor 

ooo^x/ 17,553X300 

3380 X 

220 3 X 105,534 

17,798,742,000 



= 3*5 per cent. 



5,107,845,600 

Drop of E. M. F. = 

E. M. F. X per cent, loss of power 



constant 1.49 X 



100 



220X3-5 1147-3 

= 1 - 49X -Too-=-Too- =11 - 473volts ' 

or 1 1 volts approx. 

^ , ^- w power in watts , nrw 35,106 

Current = const. 1 -25 X F ,, .. _ — = 1 -25 X —^- = 

E. M. F. 220 

199-9 amperes, or nearly 200 amperes. 



3) Tota 


I 




Total load : 


= 82 ,500 + 35 , 1 06 = 1 1 7 ,606 watts. 


Power lost 


in transformation = 






total power 




100- 


- loss in transformers 
100 




1117,606 


11,760.600 101 0yi0 




100-3 


97 



100 
E. M . F. in primary circuit = 229 X 1 *035 X 9 = 2 1 33 volts. 



ELECTRICAL ENGINEERING 345 

Cection of primary feeder in cir. mils (see the preceding 
part of this example) 

_ 82,500 X 2400 + 35, 106X3380 121.243X 1000 
121,243 2133 2 X3-5 

37,180,169,842,040,000 frtOCO . . 
= 1,930,662,801,994-5 = 19 ' 259 '"^ mils " 

Take No. 7 (B. & S.) wire = 20,817 cir. mils. 

2634X121.243X1000 „ „„ 
Per cent, power ^ 2l3 3«X20.817 =3 ' 3? P6r * 



= 87 per cent. 



Power factor = 

82,500X95 + 35 106X80 __ 10,645,980 
121,243 ~~ 121,243 

Drop of voltage in primary circuit = 

1-175X2133X3-37 nA , 
100 =84 volts. 

E. M. F of generator = 2133 + 84 =2217 volts. 

Current in primary circuit = 1-14X " = 65 amperes. 

Total copper: For lamps = ----- 559-125 lbs. 
For motors, 900 ft. No. = 

900X0-3195 = - - - - 287-55 " 
In primary circuit : 3,000 ft. 
No. 7 = 3000X0-6302= - 1890-60 •« 



Total, 2737-275 lbs. 
Cost of 2,737-275 lbs. of copper at $0.35 = $958-05. 



346 MODERN ELECTRICITY 



AN ESTIMATE 

taken from actual practice shows for a 1000 H. P. plant the 
following figures : 

Cost of plant : 

Hydraulic works with wheels, complete .... $49,732 

Power station with dynamos, complete .... 24,635 

Transmission circuit 6,200 

Pole line 3^- mile, complete 1,972 

Transformers 11 ,024 

Distributing lines, complete 21,000 

Miscellaneous 6,212 



Total, $120,775 

Operating expense per year: 

Interest and depreciation, 10 per cent. . . . $12,077 

Engineers and electrician in plant 5,100 

Linemen, teams, etc , . . 3,212 

Office expense 4,210 

Supplies and repairs 3,200 

Taxes, rent and miscellaneous . 1 ,225 

Total, $29,024 

One kilowatt hour is produced in a plant of this size at 
$0-0141. 



APPENDIX 



Corrosion of pipes by electrolysis 

The quality of electric current used in commercial electro- 
lysis, to dissolve metals in liquids, is quite frequently the cause 
of corrosion of water and gas pipes. The current employed in a 
grounded trolley system, is supposed to return through the 
bonded rails back to the dynamo in the central station ; but 
the resistance offered to the flow of current by the rails, and 
sometimes by broken rail-bonds is often so high, that the 
current leaves the rails to return to the dynamo through other 
and better conductors. Water and gas pipes possessing a large 
sectional area, offer the current a good return ; but wherever 
the current leaves a conductor in the presence of a liquid the 
surface of the conductor becomes corroded owing to the 
electrolytic quality of the current. Hence pipes under these 
circumstances soon show a rusty place where the current 
leaves them, the place enlarging with time and hollowing out 
until the pipe leaks. Rails also are corroded in the place where 
the current leaves them. 

The argument may be raised that small currents cannot 
cause very much damage ; but experiments have demonstrated 
that a steadily flowing current of one ampere, will dissolve 
nineteen pounds of iron (if in contact with liquid), during one 
year. 75 pounds of lead would be dissolved in a like manner 
under similiar conditions. At this rate, a current of 300 
amperes would corrode 5,700 pounds of iron or 22,500 pounds 
of lead in the course of one year. 

347 



348 



APPENDIX 



Fig. 158 shows a diagram of a railway, the rails of which 
have been used as the return path for the current. The cur- 
rent flows from the generator through the trolley, leaving it at 
a, passing through the motors of the car and entering the 
rails, but the pipe lying underground, in proximity to the track, 
offers the current less resistance than the rails and is entered 
by the current at b ; it then leaves the pipe at c, to flow 
through a part of the rails back to the dynamo. The car mov- 
ing, the current changes the place of entering the pipe, yet 
the point c, near the power station remains the place where 
the current leaves, and is thus subject to a constant corrosion, 
and will leak in the course of one year, or even sooner. 




tic. 158. 

Experiments have been made to protect the pipes by paint- 
ing them with asphalt and other substances, but it has been 
found that the corrosion even occurs under the coating of paint. 

Especially frequent is the corrosion of pipes in joints. Fig. 
159, represents the joint of two gas pipes A and B, through 
which a current flows in the direction of the arrow. Frequently 
owing to oxidation, it happens that the lead joint in c, offers 



APPENDIX 



349 



the current a high resistance. Then the current leaves the 

pipe A, passing through the ground and entering the pipe B, 

behind the joint, thus 

causing a ring of 

corrosion where it 

leaves the pipe to 

enter the ground (ab). 

It is therefore quite 

important not to use 

water or gas pipes as 

a part of any circuit, unless they are electrically continuous. 

To avoid such corrosion, many remedies have been tried ; 
but the best results are shown by proper bonding and 
especially by electrically welding the rails thus decreasing 
their resistance. 





Fig. 160. 

Fig. 160 shows a diagram of a railway system where 
precautions have been made against electrolytic corrosion of 
pipes. As may be observed, the current enters the trolley at 
the power station, leaves it at a, passes through the car 
motors into the rails, and enters the return feeds d and e, to 



350 APPENDIX 

return back to the generator. It may also be observed that 
there exists no electrical connection between the dynamo and 
ground ; on the contrary in practice the dynamo is carefully 
insulated from the ground, the current being carried back to 
the dynamo by special wires which at frequent intervals con- 
nect with the rails. 

The most important points to be considered when dealing 
with electrolytic corrosion of pipes, given by I. H. Farnum, 
and based upon his researches on this subject, are stated 
below. 

1 . All single trolley railways employing rails as the return 
circuit cause corrosion of pipes in their vicinity, unless special 
provisions are made to avoid it. 

2. A potential difference of a fraction of a volt between 
pipes and damp ground is sufficient to cause such corrosion. 

3. Bonding of rails with bonds of small area of section is 
insufficient to prevent the damage. 

4. Insulating of pipes from ground is insufficient to prevent 
damage and is impractical. 

5. Breaking the metallic continuity of pipes at frequent 
intervals is impractical. 

6. It is advisable to connect the positive pole of the dynamo 
to trolley. 

7. Large conductors leading from the dynamo and connect- 
ing to pipes in danger at every few hundred feet will suffi- 
ciently protect the pipes (see <of and e in fig. 1 60.) 

8. It is advisable to use separate conductors for each set of 
pipes to be protected. 

9. Connections only at power station to water and gas pipes 
are not sufficient to insure their safety. 



APPENDIX 351 

10. Connection between pipes and rails, or rail return wires 
outside of the danger district should be carefully avoided. 

11. Frequent voltage measurements between pipes and 
ground should be obtained and such changes in the return 
conductors made as the measurements indicate. 

Efficiency of dynamos and motors 

Let E = E. M. F. at motor brushes 

e = counter E. M. F. developed by the motor 

/= current flowing through the motor's armature 

r = internal resistance of the armature 

W= electrical energy delivered at brushes 

w = electrical energy lost in armature (7 2 r) 

v = electrical energy lost in field coils {I 2 f) 

E—e 

Then / = 

r 

and e = E—(IXr) 

The mechanical power developed by a motor (including power 
needed to overcome friction and power expended in eddy 
currents and hysteresis) P= eX L 

Electrical efficiency of a dynamo is the ratio of the electrical 
energy delivered at brushes, to the total energy generated, and 
equals 

W 

W+ w + v + iron and friction losses 

_ . , . Output W 

Commercial efficiency = -r-ri— = ttt-; — 

Intake W+ w 

Losses in a dynamo may be classified as follows : 

1. Mechanical losses (friction) 

2. Electrical losses (I 2 R losses in the armature and field 
coils, also losses due to hysteresis and eddy currents.) 



352 



APPENDIX 



Copper Equivalent of Steel Rails 



C. M. = 16000 X W (Weight of rail per yard). 

Example : — What is the copper equivalent of a rail weighing 65 
pounds per yard ? 

C. M. — 16000 x 65 = 1,040,000 C. M. 

That is, the rail has a conductivity equal to a copper wire of 1,040,000 
C. M., and two rails would be |equivalent to 2,000,000 CM. of 
copper. 

Metric System of Weights and Measures 

MEASURES OF LENGTHS 



1 


Millimeter = 001 


Meter = 0.0394 


Inch. 


1 


Centimeter = 0.01 


Meter = 0.3937 


Inch. 


1 


Decimeter = 0.1 


Meter = 3.937 


Inches. 


1 


Meter = 1. 


Meter = 39.37 


Inches. 


1 


Dekameter = 10. 


Meters = 393.7 


Inches. 


1 


Hectometer = 100. 


Meters = 328 Feet, 


1 Inch. 


1 


Kilometer = 1000. 


Meters = 3280 Feet, 10 Inches. 


1 


Myriameter = 10000. 


Meters = 6,2137 


Miles. 



It will be noticed that 10 Millimeters equal 1 Centimeter, 10 Centimeters 
equal 1 Decimeter, and so on. 





MEASURES OF VOLUMES 


1 


Milliliter = 


001 Liter =0.061 


Cubic Inch. 


1 


Centiliter = 


0.01 Liter = 6102 


Cubic Inch. 


1 


Deciliter = 


0.1 Liter =6.1022 


Cubic Inches. 


1 


Liter = 


1. Liter =09081 


Quart. 


1 


Dekaliter = 


10. Liters = 9.081 


Quarts. 


1 


Hectoliter = 


100. Liters = 2 Bushels, 3.35 Pecks. 


1 


Kiloliter = ' 


L000. Liters = 1.308 
WEIGHTS 


Cubic Yards. 


1 


Milligramme 


= 0.001 Gramme = 


0.0154 Grain. 


1 


Centigramme 


= 001 Gramme = 


1543 Grain. 


1 


Decigramme 


= 0.1 Gramme = 


1.5432 Grains. 


1 


Gramme 


= 1. Gramme = 


15.432 Grains. 


1 


Dekagramme 


= 10. Grammes = 


0.3527 Ounce. 


1 


Hectogramme 


= 100. Grammes = 


3.5274 Ounces. 


1 


Kilogramme 


= 1000. Grammes = 


2.2046 Pounds 


1 


Myriagramme 


= 10000. Grammes = 


22.046 Pounds 




sa sa sa &$. 




-%" 



DIAGRAM No. I j— 

TWO WIRE SYSTEM i&M) & 

FOR EXPLANATION SEE APPENDIX ^tLs^^ 







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APPENDIX 



;S3 



English and Metric Equivalents 



1 Mil = 1-1000 part of an Inch 

Circular Mils 

1 Inch 

1 Kilogramme 

1 Square Mil 

i Circular Mil 

1 Millimeter 

1 Kilogramme per Kilometer 

1 Pound per 1000 Feet 

Diameter in Millimeters 

Diameter in Mils 

Area in Square Millimeters 

Diameter in Millimeters 

Area in Square Millimeters 

Area in Circular Mils 

Pounds per 1000 Feet 

Kilogrammes per Kilometer 
Pounds per 1000 Feet 
Feet per Pound 



= .001 Inch. 

= Diameter in Mils, squared. 

= 25.4 Millimeters. 

= 2.2046 Pounds. 

= 1.2732 Circular Mils. 

= .7854 Square Mil. 

= 39.37 Mils. 

= .67196 Pound per 1000 Feet. 

= 1.4882 Kilogrammes per Kilometer 

= Diameter in Mils -+- 39-37 

= Diameter in Millimeters X 39.37 

= ( Diameter in Millimeters)^ -r- 1.273 

=l/Area in Sq. Millimeters X 1-273 
= Area in Circular Mils-s- 1973.5 
= Area in Sq. Millimeters X 1973.5 
= Weight in Kilogrammes per Kilo, 
meter-- 1.4882. [.67196 

= Weight in pounds per 1,000ft. -:- 
= Area in Circular Mils X .003027 
= 330360 -r- Circular Mils. 



Metric and English Equivalents 



Inches = 
Feet = 
Yards t= 
Miles = 
Sq. In. = 
Sq. Ft. = 
Acres = 
Cu. In. = 
Cu. Ft. = 

Lbs. Avoirdupois 
Tons (2000 lbs.) 
Lbs. per Foot 
Lbs. per Cu. Ft. 
Sq. Millimeters 
Sq. Meter 
Grammes 
Grammes 
Kilogrammes 



Millimeters -h 25.4 
Meters X 3.28083 
Meters X 1-09361 
Kilometers--- 1.60935 
Sq. Millimeters X .00155 
Sq. Meters X 10.7641 
Sq. Kilometers X 247.114 
Cu. Centimeters--16.3870 
Cubic Meters X 35.3140 

= Kilogrammes X 2.20462 
= Kilogrammes -h 907.18 
= Kilo, per Meter X .67196 
= Kilo, per Cu. Meter X .06243 
= Square Inches X 645.137 
= Square Feet X -0929 
== Ounces X 28.3495 
== Pounds X 453.5926 
= Pounds X -45359 



354 



APPENDIX 



Symbols of the More Important Metals and 
Chemicals Used in Electric Cells. 



SYMBOL. 



Fe 
Cu 
Zn 
C 

Ag 
Pb 

Hg 

CI 

H 2 O 

H 2 S0 4 

K 2 Cr 2 4 

HNO3 

Mn 2 

CuO 

Zn Cl 2 
NH 4 CI 

KOH 
Fe 2 Cl6 
Ca S0 4 
Zn S0 4 
Cd S0 4 
Pb0 2 

PbO 
Hg 2 Cl 2 
Hg S0 4 

AgCl 

CuS0 4 

H CI 



NAME. 



FORM. 



Iron 

Copper 

Zinc 

Carbon 

Silver 

Lead 

Quicksilver, Mercury 

Chlorine 

Water 

Sulphuric acid 

Potassium dichromate 

Nitric acid 

Black oxide or manganese dioxide.. 

Copper monoxide, cupric oxide, or 
Black Oxide 

Zinc chloride 

Sal-ammoniac, ammonia hydro- 
chlorate ... 

Potassium hydroxide 

Ferric chloride 

Calcium sulphate (gypsum) 

White vitriol, zinc sulphate 

Cadmium sulphate 

Lead dioxide 

Lead monoxide, litharge 

Mercurious chloride, calomel 

Mercuric sulphate 

Silver chloride 

Copper sulphate, blue vitriol 

Hydrochloric acid, hydrogen chloride 



Metals. 



metal liquid. 

green-yellow gas. 

liquid. 

liquid. 

large red crystals. 

liquid. 

ore. 

red powder, 
white powder. 

white crystals, 
white sticks, 
red crystals, 
white powder, 
long white crystals, 
yellow crystals, 
brown powder. 
Straw-colored powder 
white powdei. 

white mass. 

long blue crystals. 

liquid. 




DIAGRAM No.n 

THREE WIRE SYSTEM 

FOR EXPLAN4H0N SEE APPENDIX 



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53 




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£23 



APPENDIX 355 

Explanation of Diagram No. I, 

This diagram shows the two-wire system of distribution of 
current from bus bars of the power station generating a max- 
imum current of 300 amperes at a difference of potential 
110 volts, 

F-6, F-250, etc., indicatefuses for a maximum current of 
6,250, etc., amperes respectively. 

L-5, L-12, etc., are arc lamps requiring a current of 5, 12 
etc., amperes respectively. 

I, are incandescent lamps. 

M, are motors with their rated horse power. 

S-6, S-60, etc., are knife switches with the indicated 
maximum current for which they may be used. Single or 
double pole switches may be distinguished in the drawing, 

R, are resistances for arc lamps, etc, 

Rh, are motor starting boxes. 

C, are connecting blocks. 

H, are heaters. 

The size of wires is given in B & S. gauge — 15 — indi- 
cating No. 15 B & S., —0000— No. 0000 B. & S.- etc. 

Cables are given in circular mils — 300,000 CM. — indi- 
cating a cable of 300,000 CM. 

Explanation of Diagram No. II 

Diagram No. II, shows the three-wire system of distribu- 
tion of a current from bus bars. The same letters for 
indicating switches, motors, lamps etc., have been used as 
in Diagram No. I. 



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Engineers' Practical Test and Reference Book. 

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Ihe Machinists' and engineers' Pocket Manual. 

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Practical Application of Dynamo Electric Machinery. 

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